CN116937654B - Feedback power coordination control method for hybrid multi-feed direct current transmission system - Google Patents

Feedback power coordination control method for hybrid multi-feed direct current transmission system Download PDF

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CN116937654B
CN116937654B CN202311184665.8A CN202311184665A CN116937654B CN 116937654 B CN116937654 B CN 116937654B CN 202311184665 A CN202311184665 A CN 202311184665A CN 116937654 B CN116937654 B CN 116937654B
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hvdc
lcc
power
station
control
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CN116937654A (en
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郑子萱
张家琛
谢琦
任杰
邹轶
肖先勇
李长松
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Sichuan University
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Sichuan University
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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
    • 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
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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)
  • Control Of Electrical Variables (AREA)

Abstract

The invention discloses a feedback power coordination control method of a hybrid multi-feed direct current transmission system, which belongs to the technical field of control of the hybrid multi-feed direct current transmission system and comprises the following steps: s1, analyzing a voltage fluctuation mechanism of an alternating current bus at a transmitting end during the change of an LCC-HVDC running state, and determining a quantitative numerical relation between unbalanced power and alternating current voltage; s2, based on the determined quantitative numerical relation, aiming at accelerating the suppression of unbalanced power in the power change period, adopting multi-regulation resources to suppress the voltage fluctuation of the LCC-HVDC power transmission end alternating current bus, and realizing coordination control. The method can effectively reduce alternating current voltage fluctuation in the system power change period and improve the voltage stability of the system.

Description

Feedback power coordination control method for hybrid multi-feed direct current transmission system
Technical Field
The invention belongs to the technical field of control of a hybrid multi-feed direct current transmission system, and particularly relates to a feedback power coordination control method of a hybrid multi-feed direct current transmission system.
Background
Along with large-scale base development and utilization of new energy and large-scale direct current construction in a power system, the new energy is collected through a flexible direct current power transmission system (VSC-HVDC), and then is remotely sent out through a large-capacity conventional high-voltage direct current power transmission system (LCC-HVDC), so that the system becomes a large-scale new energy development mode with great prospect. Typical projects put into operation in China are such as Yubei back-to-back networking project, luo Ping back-to-back networking project, wu Dongde direct current transmission project and the like. The strong fluctuation of large-scale new energy sources causes frequent running state changes of conventional direct current transmission power, the response speed of a conventional mechanical switching type reactive compensation device is slower, and the instantaneous reactive unbalance of a transmitting end is caused by the mismatch of the running state rapid change and the switching speed of the reactive compensation device in the process, so that alternating voltage fluctuation is caused. The "strong-straight-weak-alternating" characteristic of the transmitting-end system further aggravates the influence of unbalanced power, and in extreme cases, system voltage instability can even be caused. Therefore, research on how to coordinate and utilize flexible regulation capability of LCC-HVDC and VSC-HVDC to inhibit alternating current voltage fluctuation in the process of switching operation states is of great significance for further improving voltage stability level of the system.
At present, a part of researches are carried out in domestic and foreign literature on the aspect of coordination control strategies of a hybrid multi-feed direct current system, and the starting point of the research is mainly to utilize VSC-HVDC flexible regulation capability to improve transient characteristics of LCC-HVDC. The literature designs a rapid reactive response module in reactive power coordination control for improving transient characteristics of LCC-HVDC (voltage source converter-high voltage direct current) side by adopting VSC-HVDC, and adds a difference value between transmission reactive power of the VSC-HVDC and transmission reactive power of the LCC-HVDC after phase change failure to VSC-HVDC fixed alternating voltage control through a PI link to improve the transient characteristics of the LCC-HVDC. The literature 'reactive coordination control strategy of the coordination of VSC and filter' is used for reducing the filter switching of the conventional direct current transmission when the transmission power is changed, and the essence of the literature is that the reactive compensation value is added to the VSC-HVDC basic control through a PI link. The literature 'transient reactive power coordination control strategy of a flexible direct current and traditional direct current interconnected power transmission system under commutation failure' provides a method for calculating a reactive power compensation value based on the slope of a triggering angle of an LCC-HVDC rectifying side after commutation failure so as to inhibit transient low voltage and overvoltage. The literature ' traditional direct current and flexible direct current transient state reactive power coordination control strategy research ' in the parallel hybrid direct current transmission system ' adds a reactive power compensation value obtained according to the turn-off angle of the LCC-HVDC inversion side to a reactive power control link of the VSC during fault.
The strategy utilizes the self-regulation capability of the VSC-HVDC, improves the operation performance of the hybrid direct current transmission system to a certain extent, but does not consider the coordination of the self-regulation capability of the VSC-HVDC and the LCC-HVDC, and the system regulation potential is not fully exerted. In addition, the existing scheme is mainly based on qualitative control of a proportional integral regulator, quantitative analysis of control instructions is lacked, and the effect of a control strategy needs to be further improved.
Disclosure of Invention
The feedback power coordination control method of the hybrid multi-feed direct current transmission system solves the problem of voltage fluctuation of the sending-end alternating current bus caused by instantaneous power unbalance during the transmission power change period of a conventional direct current transmission system in the hybrid multi-feed direct current transmission system.
In order to achieve the aim of the invention, the invention adopts the following technical scheme: a feedback power coordination control method of a hybrid multi-feed direct current transmission system comprises the following steps:
s1, analyzing a voltage fluctuation mechanism of an alternating current bus at a transmitting end during the change of an LCC-HVDC running state, and determining a quantitative numerical relation between unbalanced power and alternating current voltage;
s2, based on the determined quantitative numerical relation, aiming at accelerating the suppression of unbalanced power in the power change period, adopting multi-regulation resources to suppress the voltage fluctuation of the LCC-HVDC power transmission end alternating current bus so as to realize coordination control;
The multi-regulation resource restraining of LCC-HVDC power transmission end alternating current bus voltage fluctuation comprises the steps of utilizing a VSC-HVDC inverter station to conduct unbalanced power quantitative feedback control, utilizing an LCC-HVDC rectifier station triggering angle quantitative feedback control and utilizing an LCC-HVDC inverter station turn-off angle quantitative feedback control.
Further, in the step S1, the power and the AC voltage are unbalancedU p The quantitative numerical relation between the two is as follows:
LCC-HVDC rectifier station consuming reactive powerQ dr Active power consumed by LCC-HVDC rectifier stationI d Is in direct proportion to the firing angle of the rectifying stationαA cosine function relation;
active power consumed by an LCC-HVDC rectifier station when LCC-HVDC transmission power risesP dr Increase, inducing negative unbalanced active power, while LCC-HVDC DC currentI d Increased reactive power leading to consumption of LCC-HVDC rectifier stationQ dr The increase causes negative unbalanced reactive power, and the unbalanced reactive power and the unbalanced active power jointly cause the effective value of the alternating current bus voltage at the PCCU p Lowering;
active power consumed by an LCC-HVDC rectifier station when LCC-HVDC transmission power decreasesP dr Reduced, positive unbalanced active induced, LCC-HVDC DC current simultaneouslyI d Reduction of reactive power consumed by LCC-HVDC rectifier stationQ dr Reducing, inducing positive unbalanced reactive power, wherein the unbalanced active power and the unbalanced reactive power jointly cause the effective value of the alternating current bus voltage at the PCC U p Rising.
Further, the step S2 specifically includes:
s21, calculating an effective value of an alternating current bus voltage at the PCC based on unbalanced power generated by delay of an alternating current filter during the change of LCC-HVDC transmission power;
s22, based on the effective value of the alternating current bus voltage at the PCC, determining quantitative feedback quantity by taking the unbalanced power inhibition as a target according to the numerical relation between the unbalanced power and the alternating current voltage;
wherein the quantitative feedback quantity comprises unbalanced active quantitative feedback quantity delta of the VSC-HVDC inverter stationPAnd unbalanced reactive quantitative feedback quantity deltaQFiring angle quantitative feedback quantity of LCC-HVDC rectifier stationThe turn-off angle quantitative feedback quantity delta of LCC-HVDC inversion stationγ；
S23, based on the determined quantitative feedback quantity, utilizing the multi-regulation resource to inhibit the alternating current bus voltage fluctuation of the LCC-HVDC power transmission end, and realizing coordination control;
wherein the multi-regulated resources include VSC-HVDC inverter stations, LCC-HVDC rectifier stations, and LCC-HVDC inverter stations.
Further, in the step S23, for the VSC-HVDC inverter station, an unbalanced reactive power quantitative feedback amount Δ is provided on the basis of a fixed active power control and a fixed ac voltage controlQAc bus voltage at PCCU p Is converted into a voltage feedback value and is added to constant alternating voltage control, so that unbalanced active power quantitative feedback quantity delta PThe reactive power control side acts along with the action of the reactive power control side and is added to the fixed active power control to realize unbalanced power quantitative feedback control;
for the LCC-HVDC rectifying station, the trigger angle is quantitatively fed back by a control quantity deltaαThe trigger angle quantitative feedback control is realized in direct current control of the LCC-HVDC rectifier station foundation control;
for the LCC-HVDC inverter station, the turn-off angle is quantitatively fed back by a control quantity delta at the same time of triggering angle quantitative feedback controlγAnd the control method is added to the basic control fixed-off angle control of the LCC-HVDC inverter station to realize the quantitative feedback control of the off angle.
On the side of LCC-HVDC, the LCC-HVDC rectifying station and LCC-HVDC inversion station are comprehensively utilized, the feedback control quantity is added on the basis of constant direct current control and constant turn-off angle control, and the LCC-HVDC rectifying station is coordinated to consume reactive powerQ dr And realizing the quantitative feedback control of the trigger angle and the quantitative feedback control of the turn-off angle.
Further, in the step S23, the method for performing unbalanced power quantitative feedback control by using the VSC-HVDC inverter station specifically includes:
SA-1, and setting action dead zone section [ delta ] of unbalanced reactive power quantitative feedback controlQ H ，ΔQ L ]；
Wherein delta isQ H For unbalanced reactive power quantitative feedback control action upper limit delta Q L The lower limit of the unbalanced reactive power quantitative feedback control action is set;
SA-2, when unbalanced reactive power quantitative feedback quantity deltaQExceeding the upper and lower limit intervals [ delta ] of the operation dead zone due to the change of LCC-HVDC transmission powerQ H ，ΔQ L ]Executing an unbalanced power quantitative feedback control flow;
SA-3, reactive power quantitative feedback quantity delta of unbalanceQAc bus voltage at PCCU p The relation between the voltage feedback values is converted into voltage feedback values, the voltage feedback values are added to the VSC-HVDC inversion station, and unbalanced reactive power is controlled through alternating current voltage of a reactive power control side of the VSC-HVDC inversion station;
SA-4, following the action of reactive power control side, will unbalance active ration feedback quantity deltaPThe variation of (2) is added to the fixed active power side to control unbalanced active power, so as to realize unbalanced power quantitative feedback control.
Further, in the step SA-3, the unbalanced reactive power quantitative feedback quantity deltaQAc bus voltage at PCCU p The relation between them is:
in the method, in the process of the invention,for the ac busbar voltage at PCC under normal operating conditions, +.>Is the equivalent impedance of the alternating current system,is equivalent voltage of an alternating current system.
Further, in the step S23, the method for quantitatively feeding back the control by using the triggering angle of the LCC-HVDC rectifier station specifically includes:
SB-1, set triggerAction dead zone section [ delta ] of angle quantitative feedback control α H ,Δα L ]；
Wherein delta isα H To quantitatively feedback control the upper limit of the action, deltaα L Quantitatively feeding back a control action lower limit for the trigger angle;
SB-2, LCC-HVDC rectifier station based reactive power consumptionQ dr Firing angle with LCC-HVDC rectifier stationαThe relation between the trigger angle and the quantitative feedback quantity is determinedAnd fed back to the LCC-HVDC rectification station;
SB-3, quantitative feedback quantity based on determined firing angleRegulating the rectifier station firing angle +.>Regulating reactive power consumption of LCC-HVDC rectifier stationQ dr And the quantitative feedback control of the trigger angle is realized.
Further, in the step SB-2:
LCC-HVDC rectifier station consuming reactive powerQ dr Firing angle with LCC-HVDC rectifier stationThe relation between them is:
in the method, in the process of the invention,active power consumed for LCC-HVDC rectifier station, +.>For equivalent reactance of each phase of the rectifying station, +.>For LCC-HVDC rectifier inversion side direct current, +.>The method comprises the steps of (1) obtaining an effective value of a valve side no-load line voltage of a converter transformer of a rectifying station;
quantitative feedback quantity of determined trigger angleThe method comprises the following steps:
in the method, in the process of the invention,reactive power variation is consumed for LCC-HVDC rectification during transmission power variation, +.>Active power variation for LCC-HVDC rectifier station consumption during transmission power variation, +.>For LCC-HVDC DC variation during transmission power variation, wherein +. >，/>，/>，/>For the active power consumed by the LCC-HVDC rectifier station in normal operating conditions +.>Active power consumed for LCC-HVDC rectifier stations,for reactive power consumed by the LCC-HVDC rectifier station in normal operating conditions +.>Reactive power consumed for LCC-HVDC rectifier station, +.>For LCC-HVDC DC under normal operating conditions, +.>Is LCC-HVDC direct current.
Further, in the step S23, at the start angle of the rectification stationAnd the control method is characterized in that the turn-off angle quantitative feedback control is carried out by using the LCC-HVDC inverter station while the adjustment is carried out, and the control method specifically comprises the following steps:
SC-1, and an operation dead zone section [ delta ] for setting off angle quantitative controlγ H ，Δγ L ]；
Wherein delta isγ H For the upper limit of the action of the turn-off angle quantitative control, deltaγ L A lower limit of the action for quantitatively controlling the turn-off angle;
SC-2, LCC-HVDC inverter station based reactive powerQ di Off angle with LCC-HVDC inverter stationγDetermining the off-angle quantitative feedback control quantity delta from quantitative numerical relation of (2)γAnd fed back to the LCC-HVDC inverter station;
SC-3, quantitative feedback control quantity delta at off-angle during LCC-HVDC transmission power variationγExceeding the action dead zone interval [ delta ]γ H ，Δγ L ]When according to deltaγThe LCC-HVDC inversion station adopts a mode of controlling a fixed turn-off angleγAdjusting, thereby adjusting the reactive power consumption of the LCC-HVDC rectifier station Q dr And the quantitative feedback control of the turn-off angle is realized.
Further, in the step SC-2, the off angle is quantitatively fed back by the control amount deltaγThe method comprises the following steps:
in the method, in the process of the invention,reactive power variation for LCC-HVDC inverter station consumption during transmission power variation, +.>Active power variation for LCC-HVDC inverter station consumption during transmission power variation, +.>For the commutation reactance of an LCC-HVDC inverter station,/->The method comprises the steps of (1) setting an effective value of a valve-side no-load line voltage of a converter transformer of an LCC-HVDC inverter station; wherein (1)>，，/>Reactive power consumed by LCC-HVDC inverter station under normal operation condition +.>Reactive power consumption for LCC-HVDC inverter station, < >>For the active power consumed by the LCC-HVDC inverter station under normal operating conditions +.>Is the active power of the LCC-HVDC inverter station.
The beneficial effects of the invention are as follows:
1) The unbalanced power quantitative feedback coordination control method comprehensively utilizes the multi-regulation resources of the VSC-HVDC inverter station, the LCC-HVDC rectifier station and the inverter station, improves the problems of single control of the VSC-HVDC and coordination of the conventional direct current and the flexible direct current, and reduces the regulation pressure of each power regulation resource; and the reactive power and active compensation values of the VSC-HVDC inversion station, the trigger angle compensation value of the LCC-HVDC rectification station and the turn-off angle compensation value of the LCC-HVDC inversion station are determined, so that compared with the additional control performed through a PI link, the control response speed and the control precision of the system during the transmission power change period are improved, and the control effect is improved.
2) The unbalanced power quantitative feedback coordination control method provided by the invention is still effective and applicable under different variation degrees of LCC-HVDC transmission power. The proposed strategy may further improve the control effect with increasing VSC-HVDC operating capacity or decreasing electrical distance, affected by factors such as VSC-HVDC operating capacity and tie length.
Drawings
Fig. 1 is a flowchart of a feedback power coordination control method of a hybrid multi-feed direct current transmission system provided by the invention.
Fig. 2 is a block diagram of a hybrid multi-feed dc power transmission system provided by the present invention.
Fig. 3 is an equivalent circuit model diagram of the hybrid multi-feed direct current transmission system provided by the invention.
Fig. 4 is a simulation waveform of the system under the condition of reduced LCC-HVDC transmission power.
Fig. 5 is a simulation waveform of the system at different reduction degrees of LCC-HVDC transmission power provided by the present invention.
Fig. 6 is a simulation waveform of a system under the working condition of increasing the transmission power of LCC-HVDC.
Fig. 7 is a simulation waveform of a system with different rising degrees of LCC-HVDC transmission power provided by the present invention.
Fig. 8 shows simulation waveforms of the system under different capacities of the VSC-HVDC.
FIG. 9 is a diagram of simulated waveforms of the system at different electrical distances provided by the present invention.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and all the inventions which make use of the inventive concept are protected by the spirit and scope of the present invention as defined and defined in the appended claims to those skilled in the art.
Example 1:
the embodiment of the invention provides a feedback power coordination control method of a hybrid multi-feed direct current transmission system, which is used for accelerating and restraining the voltage fluctuation of a transmitting-end alternating current bus caused by instantaneous power unbalance during the change of conventional direct current transmission power. Specifically, as shown in fig. 1, the coordination control method in the embodiment of the invention includes the following steps:
s1, analyzing a voltage fluctuation mechanism of an alternating current bus at a transmitting end during the change of an LCC-HVDC running state, and determining a quantitative numerical relation between unbalanced power and alternating current voltage;
s2, based on the determined quantitative numerical relation, aiming at accelerating the suppression of unbalanced power in the power change period, adopting multi-regulation resources to suppress the voltage fluctuation of the LCC-HVDC power transmission end alternating current bus so as to realize coordination control;
The multi-regulation resource restraining of LCC-HVDC power transmission end alternating current bus voltage fluctuation comprises the steps of utilizing a VSC-HVDC inverter station to conduct unbalanced power quantitative feedback control, utilizing an LCC-HVDC rectifier station triggering angle quantitative feedback control and utilizing an LCC-HVDC inverter station turn-off angle quantitative feedback control.
In the embodiment of the invention, in the process of analyzing the voltage fluctuation mechanism of the transmission-end alternating current bus during the change of the LCC-HVDC running state, for simplifying analysis, the hybrid multi-feed direct current transmission system shown in figure 2 is simplified, the equivalent circuit model is shown in figure 3, and the local power network comprising the alternating current collecting wind power plant is uniformly represented as a voltage source with reactance by using the Thevenin equivalent method; the ac filter and reactive compensator are represented by capacitors.
In figure 3 of the present embodiment of the drawings,U e 、U p 、U i respectively at the equivalent voltage and PCC of the alternating current systemAn LCC-HVDC inversion side alternating current bus voltage effective value;U dr 、U di 、I d direct current voltages and direct current at the rectification side and the inversion side of the LCC-HVDC respectively;P ac 、Q ac 、P vsc 、Q vsc the total active power, the total reactive power and the active power and the reactive power transmitted by the VSC are respectively provided for the alternating current system;P dr 、Q dr 、P di 、Q di active power and reactive power consumed by the LCC-HVDC rectifier station and active power and reactive power of the LCC-HVDC inverter station respectively; Q cr 、Q ci Reactive power provided for the rectifier station filter and the inverter station filter respectively;X e equivalent reactance of an alternating current system;X L is the tie reactance. DeltaPAnd deltaQIs the unbalanced active power and the unbalanced reactive power injected into the alternating current system.
The power relationship of the ac-dc system is as follows:
normally, delta in FIG. 3PAnd deltaQAll zero, assuming that the VSC remains in constant active and reactive control operation, when the LCC-HVDC transmission power varies, due toP dr AndQ dr change in deltaPAnd deltaQCorresponding changes may occur. Thus, the first and second substrates are bonded together,U p can deviate from the rated value, and the changed value can passU e And (5) calculating. DeltaPAnd deltaQThe following relationship is satisfied, where the subscript N is a value under normal conditions.
In the formula deltaQ 1 For reactive power loss on equivalent reactance of an alternating current system, the filter is assumed to be inactive due to delay,Q cr 、ΔQ 1 can be expressed as:
assume thatU e Is constant, thenU p Can be expressed as
Solving the above equation to calculateU p Due to deltaQAnd deltaPAll of the changes in (a) will result inU p But the former is the dominant factor. Therefore, analysis of ac busbar voltage fluctuations due to LCC-HVDC operating state changes should focus on reactive power consumption by the rectifier stationsQ dr According to a quasi-steady state model of LCC-HVDC, Q dr Can be expressed as:
in the method, in the process of the invention,Nfor a number of 6 ripple converters in each pole of the converter station,Tfor the turns ratio of the converter transformer,αfor the firing angle of the rectifying station,X r1 is the equivalent reactance of each phase of the rectifying station.
In the present embodiment, as can be seen from the above formula, the dc sideQ dr Mainly composed ofI d Andαand (5) determining. Adjustment of actual LCC-HVDC operating Power by modulationNodeI d The transformer tap is matched with the action of the transformer tap; based on this, in step S1 of the present embodiment, the power and the ac voltage are unbalancedU p The quantitative numerical relation between the two is as follows:
LCC-HVDC rectifier station consuming reactive powerQ dr Active power consumed by LCC-HVDC rectifier stationIs in direct proportion to the firing angle of the rectifying stationαA cosine function relation;
active power consumed by an LCC-HVDC rectifier station when LCC-HVDC transmission power risesP dr Increase, inducing negative unbalanced active power, while LCC-HVDC DC currentI d Increased reactive power leading to consumption of LCC-HVDC rectifier stationQ dr The increase causes negative unbalanced reactive power, and the unbalanced reactive power and the unbalanced active power jointly cause the effective value of the alternating current bus voltage at the PCCU p Lowering;
active power consumed by an LCC-HVDC rectifier station when LCC-HVDC transmission power decreasesP dr Reduced, positive unbalanced active induced, LCC-HVDC DC current simultaneously I d Reduction of reactive power consumed by LCC-HVDC rectifier stationQ dr Reducing, inducing positive unbalanced reactive power, wherein the unbalanced active power and the unbalanced reactive power jointly cause the effective value of the alternating current bus voltage at the PCCU p Rising.
Therefore, the key to suppressing the ac voltage ripple at the supply during the change of the operating state is to eliminate the unbalanced power of the system.
In the embodiment of the invention, based on the analysis in the step S1, the unbalanced power generated in the LCC-HVDC operation state adjustment process is a direct cause of the voltage fluctuation of the converter bus. Therefore, if the unbalanced power delta between the transmitting-end alternating current system and the high-voltage direct current system can be eliminated based on the quantitative numerical relation between the instantaneous unbalanced power and the alternating current voltage by comprehensively utilizing three adjustment resources of the VSC-HVDC inversion station, the LCC-HVDC rectification station and the LCC-HVDC inversion stationQAnd deltaPNot only can reduce each adjustment resourceThe effect of suppressing voltage fluctuation can be improved; therefore, step S2 of the embodiment of the present invention specifically includes:
s21, calculating an effective value of an alternating current bus voltage at the PCC based on unbalanced power generated by delay of an alternating current filter during the change of LCC-HVDC transmission power;
S22, based on the effective value of the alternating current bus voltage at the PCC, determining quantitative feedback quantity by taking the unbalanced power inhibition as a target according to the numerical relation between the unbalanced power and the alternating current voltage;
wherein the quantitative feedback quantity comprises unbalanced active quantitative feedback quantity delta of the VSC-HVDC inverter stationPAnd unbalanced reactive quantitative feedback quantity deltaQThe triggering angle quantitative feedback quantity delta of LCC-HVDC rectifier stationαThe turn-off angle quantitative feedback quantity delta of LCC-HVDC inversion stationγ；
S23, based on the determined quantitative feedback quantity, utilizing the multi-regulation resource to inhibit the alternating current bus voltage fluctuation of the LCC-HVDC power transmission end, and realizing coordination control;
wherein the multi-regulated resources include VSC-HVDC inverter stations, LCC-HVDC rectifier stations, and LCC-HVDC inverter stations.
In step S23 in the present embodiment, for the VSC-HVDC inverter station, an unbalanced reactive power quantitative feedback amount Δ is provided on the basis of a fixed active power control and a fixed ac voltage controlQAc bus voltage at PCCU p Is converted into a voltage feedback value to be added to a constant alternating voltage control, and unbalanced active and quantitative feedback quantity deltaPThe reactive power control side acts along with the action of the reactive power control side and is added to the fixed active power control to realize unbalanced power quantitative feedback control;
For the LCC-HVDC rectifying station, the trigger angle is quantitatively fed back by a control quantity deltaαThe trigger angle quantitative feedback control is realized in direct current control of the LCC-HVDC rectifier station foundation control;
for the LCC-HVDC inverter station, the turn-off angle is quantitatively fed back by a control quantity delta at the same time of triggering angle quantitative feedback controlγAnd the control method is added to the basic control fixed-off angle control of the LCC-HVDC inverter station to realize the quantitative feedback control of the off angle.
Specifically, in step S23 of the present embodiment, the method for unbalanced power quantitative feedback control using the VSC-HVDC inverter station is specifically:
SA-1, and setting action dead zone section [ delta ] of unbalanced reactive power quantitative feedback controlQ H ，ΔQ L ]；
Wherein delta isQ H For unbalanced reactive power quantitative feedback control action upper limit deltaQ L The lower limit of the unbalanced reactive power quantitative feedback control action is set;
SA-2, when unbalanced reactive power quantitative feedback quantity deltaQExceeding the upper and lower limit intervals [ delta ] of the operation dead zone due to the change of LCC-HVDC transmission powerQ H ，ΔQ L ]Executing an unbalanced power quantitative feedback control flow;
SA-3, reactive power quantitative feedback quantity delta of unbalanceQAc bus voltage at PCCU p The relation between the voltage feedback values is converted into voltage feedback values, the voltage feedback values are added to the VSC-HVDC inversion station, and unbalanced reactive power is controlled through alternating current voltage of a reactive power control side of the VSC-HVDC inversion station;
SA-4 for feeding back unbalance active ration delta based on the action of reactive power control sidePThe variation of (2) is added to the fixed active power side to control unbalanced active power, so as to realize unbalanced power quantitative feedback control.
Specifically, in order to avoid controlling frequent actions, the upper and lower limits of the action dead zone of the unbalanced power quantitative feedback control are set, when deltaQExceeding the upper and lower limit intervals [ delta ] of the operation dead zone due to the change of LCC-HVDC transmission powerQ H ，ΔQ L ]When build deltaQTo be added to constant AC voltage control, delta, in relation to AC bus voltage at PCCPAnd also acts with the action of the reactive power control side, and is added to the fixed active power control. DeltaQAnd deltaPIs added quantitatively to enable the reactive current reference value of the inner loop of the VSC inverter stationi qref And VSC-HVDC inverter station inner loop active current reference valuei dref The response rate of the system is further improved on the original basis, and the VSC-HVDC is better utilized to inhibit instantaneous unbalanced power.
Specifically, in the step SA-3, the unbalanced reactive power quantitative feedback quantity deltaQAc bus voltage at PCCU p The relation between them is:
in the method, in the process of the invention,for the ac busbar voltage at PCC under normal operating conditions, +.>Is the equivalent impedance of the alternating current system,is equivalent voltage of an alternating current system.
In step S23 of the present embodiment, the trigger angle quantitative feedback control of the LCC-HVDC rectifier station is performed according to αAndQ dr the relation between the two is known to follow the change rule of cosine function, and LCC-HVDC steady state operation is carried outα=17°. During the reduction of the LCC-HVDC transmission power,Q dr reduced filter action delay without overcompensation by reducingαCan enableQ dr Increasing, consuming part of surplus reactive power, whereas when the LCC-HVDC transmission power rises, the method can be realized by increasingαTo makeQ dr And the reactive power under compensation of the filter is relieved.
Based on this, the method for implementing the triggering angle quantitative feedback control in step S23 specifically includes:
SB-1, action dead zone section [ delta ] for setting triggering angle quantitative feedback controlα H ,Δα L ]；
Wherein delta isα H To quantitatively feedback control the upper limit of the action, deltaα L Quantitatively feeding back a control action lower limit for the trigger angle;
SB-2, LCC-HVDC rectifier station based reactive power consumptionQ dr Firing angle with LCC-HVDC rectifier stationαRelationship between each other, determineQuantitative feedback quantity delta of trigger angleαAnd fed back to the LCC-HVDC rectification station;
SB-3, quantitative feedback quantity delta based on determined firing angleαRegulating the firing angle of a rectifier station by means of a fixed direct current through an LCC-HVDC rectifier stationαRegulating reactive power consumption of LCC-HVDC rectifier stationQ dr And the quantitative feedback control of the trigger angle is realized.
In step SB-2 of the present embodiment, there is a model according to the LCC-HVDC quasi-steady-state mathematical model
In the method, in the process of the invention,U d0r for the ideal no-load dc voltage at the rectifying side,φ r for the power factor angle of the rectifying station,U 1 the effective value of the valve side no-load line voltage of the converter transformer of the rectifying station is obtained. From this, it can be seen that the LCC-HVDC rectifier station consumes reactive powerQ dr Firing angle with LCC-HVDC rectifier stationαThe relation between them is:
in the method, in the process of the invention,active power consumed for LCC rectification station, < >>For equivalent reactance of each phase of the rectifying station, +.>For LCC-HVDC rectifier inversion side direct current, +.>Effective voltage of valve side no-load line of converter transformer of rectifying stationThe value of the sum of the values,
when an unbalanced power occurs in LCC-HVDC there is a relation where the subscript N is a value under normal conditions.
The quantitative feedback quantity of the determined trigger angle is obtainedThe method comprises the following steps:
in the method, in the process of the invention,reactive power variation is consumed for LCC-HVDC rectification during transmission power variation, +.>Active power variation for LCC-HVDC rectifier station consumption during transmission power variation, +.>For LCC-HVDC DC variation during transmission power variation, wherein +.>，/>，/>，/>For the active power consumed by the LCC-HVDC rectifier station in normal operating conditions +.>Active power consumed for LCC-HVDC rectifier stations,for reactive power consumed by the LCC-HVDC rectifier station in normal operating conditions +.>Reactive power consumed for LCC-HVDC rectifier station, +. >For LCC-HVDC DC under normal operating conditions, +.>Is the inversion side direct current of the LCC-HVDC rectifier.
In the present embodiment, by controllingαReactive power consumption of the LCC-HVDC rectifying side is changed, reactive power pressure of the VSC inverter station can be regulated, and the effect of inhibiting unbalanced power is improved.
In step S23 of the embodiment of the present invention, the trigger angle of the rectification stationαAt the same time of regulation, in the process of quantitatively feeding back control of the turn-off angle by using the LCC-HVDC inverter station, the direct current of the LCC-HVDC system can be expressed as follows:
in the method, in the process of the invention,Ris a direct current loop resistance, composed ofQ dr The expression is such that,I d and (3) withQ dr Approximately proportional, as can be seen from the above equation, the DC current is proportional toU dr AndU di is a difference delta of (1)UWhen the LCC-HVDC transmission power is changed,U dr andU di the same trend changes occur. LCC-HVDC inversion station adopting fixed turn-off angleControl by adjustingγControllable DC voltage, varying deltaUThereby adjusting the DC currentI d So adjustαIs adjusted simultaneously and cooperativelyγReactive power consumption of LCC-HVDC can be quickly regulated, and pair of LCC-HVDC rectifier stations is reducedQ dr Further improving the control effect and the response speed.
For LCC-HVDC inversion side
In the method, in the process of the invention,U d0i for an ideal no-load dc voltage on the inverter side, X r2 Is the commutation reactance of the inversion station.
In consideration of communication delay existing between LCC-HVDC rectifier station and inverter station, the local information measurement pair of inverter station during the change of LCC-HVDC transmission power in the embodimentγThe quantitative feedback control is carried out, and the control method specifically comprises the following steps:
SC-1, and an operation dead zone section [ delta ] for setting off angle quantitative controlγ H ，Δγ L ]；
Wherein delta isγ H For the upper limit of the action of the turn-off angle quantitative control, deltaγ L A lower limit of the action for quantitatively controlling the turn-off angle;
SC-2, LCC-HVDC inverter station based reactive powerQ di Off angle with LCC-HVDC inverter stationγDetermining the off-angle quantitative feedback control quantity delta from quantitative numerical relation of (2)γAnd fed back to the LCC-HVDC inverter station;
SC-3, quantitative feedback control quantity delta at off-angle during LCC-HVDC transmission power variationγExceeding the action dead zone interval [ delta ]γ H ，Δγ L ]When according to deltaγThe LCC-HVDC inversion station adopts a mode of controlling a fixed turn-off angleγAdjusting, thereby adjusting LCC-HVDC rectifier station consumptionReactive powerQ dr And the quantitative feedback control of the turn-off angle is realized.
In step SC-2 of the present embodiment, when determining the off-angle quantitative feedback control amount, the inverter station has the following relationship with the rectifier station similarly:
in the method, in the process of the invention,φ i for the power factor angle of the inverter station,U 2 the method comprises the steps of (1) obtaining an effective value of a valve side no-load line voltage of a converter transformer of an inversion station; thereby obtaining the off angle quantitative feedback control quantity delta γThe method comprises the following steps:
in the method, in the process of the invention,reactive power variation for LCC-HVDC inverter station consumption during transmission power variation, +.>Active power variation for LCC-HVDC inverter station consumption during transmission power variation, +.>For the commutation reactance of an LCC-HVDC inverter station,/->For LC (liquid crystal)The valve side no-load line voltage effective value of the converter transformer of the C-HVDC inverter station; wherein (1)>，，/>Reactive power consumed by LCC-HVDC inverter station under normal operation condition +.>Reactive power for LCC-HVDC inverter station, < >>For the active power consumed by the LCC-HVDC inverter station under normal operating conditions +.>Is the active power of the LCC-HVDC inverter station.
Quantitatively feeding back the turn-off angle by a control amount deltaγThe method is added to the control of the fixed off angle of the LCC-HVDC inverter station, so that the change rate of the off angle is further improved on the basis of the prior art, and the response speed of the LCC-HVDC inverter side to unbalanced power inhibition is accelerated.
Example 2:
this example is to verify the effectiveness of the unbalanced power quantitative feedback control method in example 1;
in this embodiment, a simulation model of the hybrid multi-feed dc power transmission system shown in fig. 2 is built in the PSCAD/EMTDC. During normal operation, the voltage at the PCC is 345kV, the LCC-HVDC running power is 1000MW, the VSC running power is 400MW, the short circuit ratio of the local weak alternating current system is 2.5, the transmission power is 600MW, and the power balance at the PCC is stable. Setting delta in consideration of fluctuation of reactive power of system in actual stable operation Q H =20 Mvar and ΔQ L -20Mvar. Setting [ delta ]α H ，Δα L ]Is [2.5 DEG, -2.5 DEG ]]，[Δγ H ，Δγ L ]Is [1 DEG, -1 DEG ]]. LCC-HVDC and VSpecific parameters of the SC-HVDC are shown in tables 1 and 2.
Table 1: LCC-HVDC System principal parameters
System parameter values
Rated power 1000MW
Operating power 1000MW
Rated voltage at rectifying side 345kV
Rated voltage of inversion side 230kV
Rated DC voltage 500kV
Rated current 2kA
Reactive compensation capacity 625Mvar
Table 2: main parameters of VSC-HVDC system
System parameter values
Rated capacity 450MVA
Operating power 400MW
Rated voltage at rectifying side 345kV
Rated voltage at inversion side 345kV
Rated DC voltage 400kV
In the unbalanced power quantitative feedback coordination control strategy provided in this embodiment, the triggering angle quantitative feedback value of the triggering angle quantitative feedback control of the LCC-HVDC rectifier station and the turn-off angle quantitative feedback value of the turn-off angle quantitative feedback control of the LCC-HVDC inverter station can be obtained by calculating local power flow information, for the VSC-HVDC unbalanced power quantitative feedback control, inter-station signal transmission is required, the electrical distance between the VSC-HVDC inverter station and the LCC-HVDC rectifier station is very close, so that the communication delay effect can be considered to be smaller, the first-order inertia link is set to simulate the communication delay of the VSC-HVDC inverter station and the LCC-HVDC rectifier station, and the ratio coefficient is set GTime coefficient =1.0T=0.01s。
Based on the above parameter settings, the present embodiment performs control strategy analysis from the following aspects:
1. LCC-HVDC transmission power reduction condition analysis
Under the working condition, four different control schemes are set, and the effectiveness of the proposed control strategy is verified through comparative analysis.
Scheme 1: the VSC-HVDC reactive control adopts fixed reactive power control, and the LCC-HVDC adopts default control.
Scheme 2: the VSC-HVDC reactive control adopts constant alternating voltage control, and the LCC-HVDC adopts default control.
Scheme 3: and a rapid reactive response control strategy is adopted, on the basis of fixed alternating voltage control, the difference value of VSC-HVDC and LCC-HVDC transmission reactive power in the transmission power change period is added to the fixed alternating voltage control through a PI link, and the LCC-HVDC adopts default control.
Scheme 4: the unbalanced power quantitative feedback coordination control strategy provided by the invention is adopted.
The LCC-HVDC dc current command was reduced from 1.0p.u. to 0.7p.u. at 3s, the simulated waveform is shown in fig. 4.
In terms of control effect, as can be seen from fig. 4 (a), (c) and (d), when the LCC-HVDC transmission power is reduced, the LCC-HVDC converter station consumption reactive power is reduced in scheme 1, the reactive power provided by the filter has not yet been matched with the reactive power consumed by the converter station, and the excess reactive power provided by the filter is injected into the ac system to act together with the unbalanced active power, so that the voltage at the PCC is increased up to 1.143p.u., and the unbalanced reactive power reaches 345.485Mvar at maximum. For scheme 2 and scheme 3, the VSC-HVDC receiving end adopts constant alternating voltage control, after the voltage at PCC exceeds the setting value due to unbalanced power, the VSC-HVDC inverter station absorbs excessive reactive power for inhibiting overvoltage, and scheme 3 is based on scheme 2, the response rate of the VSC-HVDC reactive power is accelerated by adding the difference value between the VSC-HVDC and LCC-HVDC reactive power through PI link, and the two are respectively carried out U p The maximum value of the unbalanced reactive power is reduced from 1.143p.u. to 1.073p.u. and 1.037p.u., and the maximum value of the unbalanced reactive power is respectively reduced from 345.485Mvar to 126.039Mvar and 34.530Mvar. For scheme 4, the vsc inverter station pair deltaQAnd deltaPThe reactive power consumption of the LCC-HVDC rectifying station is increased by respectively and quickly adjusting the triggering angle and the turn-off angle of the LCC-HVDC rectifying station and the inversion station to share the unbalanced power adjusting pressure,U p up to 1.014p.u., unbalanced reactive power up to 20.769Mvar, while simultaneously taking account of the suppression of unbalanced active power, the proposed strategy is more accurate for instantaneous unbalanced power than schemes 2 and 3And (5) quantitatively compensating.
In terms of comprehensive regulation of resources, as can be seen from fig. 4 (b), (e) and (f), compared with the schemes 2 and 3, the reactive power absorbed by the VSC-HVDC is less in scheme 4, the reactive power regulation pressure of the VSC-HVDC is reduced, the triggering angle of the LCC-HVDC rectifying side is regulated to a corresponding setting value according to a determined numerical relationship under the coordinated control of the off angle of the inverter side, the reactive power consumption of the rectifying station is increased, and meanwhile, the excessive drop of the triggering angle for realizing the control effect is relieved, so that the strategy provided by the invention can comprehensively utilize the multi-regulation resources and reduce the power regulation pressure of each rectifying station.
In terms of response speed, as can be seen from FIG. 4, scheme 4 is compared with schemes 2, 3U p And deltaQThe peak value is reached in a shorter time, the response speed of the VSC-HVDC absorbing reactive power is faster, and meanwhile, the LCC-HVDC triggering angle and the turn-off angle are quickly adjusted to corresponding setting values in the power change period, so that the proposed strategy can respond to unbalanced power more.
To further verify the effectiveness and applicability of the proposed strategy in the case of different levels of power reduction of LCC-HVDC transmission, simulation analysis was performed on the four schemes using different levels of power reduction instructions, and the simulation waveforms are shown in FIG. 5, so that it can be seen that the four schemes are followed by an increase in the amplitude of the power reduction instructionsU p The highest value will also rise, but scheme 4 has the best control effect compared with other schemes, and the response speed is faster,U p the fluctuation amplitude is limited within + -0.05 p.u. and shows that the proposed strategy has more excellent control effect under different transmission power drop amplitudes.
2. LCC-HVDC transmission power ramp-up condition analysis
Under this condition, the same four schemes as described above are employed. The LCC-HVDC dc command set at 3s rises from 1.0p.u. to 1.1p.u., with the simulated waveforms shown in fig. 6.
In terms of control effect, as can be seen from fig. 6 (a), (c) and (d), when the LCC-HVDC transmission power increases, the LCC-HVDC converter station consumption reactive power increases under scheme 1, the reactive power provided by the filter does not match the reactive power consumed by the converter station yet, and the acThe system injects reactive power into the LCC-HVDC rectifier station to act together with unbalanced active power to reduce the voltage at the PCC to 0.944p.u., and the unbalanced reactive power reaches 131.542Mvar at maximum. For scheme 2 and scheme 3, both will be respectivelyU p The lowest value is increased from 0.944p.u. to 0.965p.u., and the unbalanced reactive power maximum value is decreased from 131.542Mvar to 83.800Mvar, 26.585Mvar, respectively. With respect to scheme 4 of the present invention,U p the maximum value is increased to 0.994p.u., the maximum value of unbalanced reactive power is reduced to 17.170Mvar, and the proposed strategy can more accurately quantitatively compensate instantaneous unbalanced power as the same as the power is reduced when the transmission power is increased.
In terms of comprehensive adjustment of resources, as can be seen from fig. 6 (b), (e) and (f), compared with the solutions 2 and 3, the reactive power of VSC-HVDC is less, the reactive power adjustment pressure of VSC-HVDC is reduced, the triggering angle of the LCC-HVDC rectifying side is adjusted to a corresponding setting value according to a determined numerical relationship under the coordinated control of the off angle of the inverting side, the reactive power consumption of the rectifying station is reduced, and the excessive rise of the triggering angle for realizing the control effect is relieved.
In terms of response speed, as can be seen from FIG. 6, scheme 4 is compared with schemes 2, 3U p And deltaQThe minimum value is reached in a shorter time, the response speed of the VSC-HVDC to generate reactive power is faster, and the LCC-HVDC trigger angle and the turn-off angle are quickly adjusted to corresponding setting values during the power change period, so that the proposed strategy can respond to unbalanced power more as the power is reduced when the transmission power is increased.
To further verify the effectiveness and applicability of the proposed strategy in different levels of power rise of LCC-HVDC transmission, simulation analysis was performed on the four schemes using different levels of power rise command, the simulation waveforms are shown in FIG. 7, and it can be seen that as the amplitude of the power rise command increases, the power rise command is increased under the four schemesU p The minimum value will also decrease, but scheme 4 has the best control effect compared with other schemes, and the response speed is faster,U p the fluctuation amplitude is limited to within + -0.05 p.uThe proposed strategy is shown to have a more excellent control effect at different rise amplitudes of the transmission power.
3. VSC-HVDC (voltage source converter-high voltage direct current) transmission capacity different simultaneous control effect analysis
To verify the effectiveness and applicability of the proposed strategy under different VSC-HVDC capacities, the VSC-HVDC operating capacities were chosen to be 30%, 50% and 70% of the LCC-HVDC operating capacity, respectively, i.e P vsc =300MW、P vsc =500 MW sumP vsc Control effect of the proposed strategy was analyzed in LCC-HVDC transmission power down-and up-running conditions =700 MW, simulation results are shown in fig. 8.
As can be seen from fig. 8 (a) and (b), the proposed strategy can still well suppress ac busbar voltage fluctuations generated at the LCC-HVDC transmission end during transmission power changes when the VSC-HVDC operating capacity is changed, and as the VSC-HVDC operating capacity increases, the proposed strategy results in transmission power changesU p The surge suppression effect becomes better, which means that the improvement of the running capacity enhances the ability of the VSC-HVDC receiving end to adjust unbalanced reactive power.
4. Influence of the Electrical distance of the two stations on the control Effect
To verify the effect of the electrical distances between the VSC-HVDC inverter station and the LCC-HVDC rectifier station on the control effect of the proposed control strategy, the electrical distances between the two stations are 20km,40km and 60km, the control effect of the proposed strategy is analyzed under the descending working condition and the ascending working condition of the LCC-HVDC transmission power respectively, and the simulation waveforms are shown in figure 9.
It can be seen from 9 (a) and 9 (b) that the proposed strategy can still well inhibit the ac busbar voltage fluctuation generated by the LCC-HVDC transmitting end during the transmission power change when the electrical distance between two stations is changed, and the proposed strategy can reduce the transmission power change along with the reduction of the electrical distance U p The wave suppression effect becomes better, which means that when the electric distance between the LCC-HVDC and the VSC-HVDC system is larger, the loss on the connecting line is larger, so that the influence of the VSC-HVDC system on the LCC-HVDC is reduced, and the proposed coordination strategy can more effectively exert the excellent performance of the VSC-HVDC in engineering application with the actual LCC-HVDC rectifier station and the VSC-HVDC inverter station with the closer distanceThe potential suppresses transient voltage disturbances of LCC-HVDC caused by variations in transmission power.
The principles and embodiments of the present invention have been described in detail with reference to specific examples, which are provided to facilitate understanding of the method and core ideas of the present invention; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present invention, the present description should not be construed as limiting the present invention in view of the above.
Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations from the teachings of the present disclosure without departing from the spirit thereof, and such modifications and combinations remain within the scope of the present disclosure.

Claims (7)

1. The feedback power coordination control method of the hybrid multi-feed direct current transmission system is characterized by comprising the following steps of:
s1, analyzing a voltage fluctuation mechanism of an alternating current bus at a transmitting end during the change of an LCC-HVDC running state, and determining a quantitative numerical relation between unbalanced power and alternating current voltage;
s2, based on the determined quantitative numerical relation, aiming at accelerating the suppression of unbalanced power in the power change period, adopting multi-regulation resources to suppress the voltage fluctuation of the LCC-HVDC power transmission end alternating current bus so as to realize coordination control;
the multi-regulation resource restraining LCC-HVDC power transmission end alternating current bus voltage fluctuation comprises the steps of carrying out unbalanced power quantitative feedback control by utilizing a VSC-HVDC inversion station, carrying out triggering angle quantitative feedback control by utilizing the LCC-HVDC inversion station, and carrying out turn-off angle quantitative feedback control by utilizing the LCC-HVDC inversion station;
the step S2 specifically comprises the following steps:
s21, calculating an effective value of an alternating current bus voltage at the PCC based on unbalanced power generated by delay of an alternating current filter during the change of LCC-HVDC transmission power;
s22, based on the effective value of the alternating current bus voltage at the PCC, determining quantitative feedback quantity by taking the unbalanced power inhibition as a target according to the numerical relation between the unbalanced power and the alternating current voltage;
Wherein the quantitative feedback quantity comprises unbalanced active quantitative feedback quantity delta of the VSC-HVDC inverter stationPAnd unbalanced reactive quantitative feedback quantity deltaQThe triggering angle quantitative feedback quantity delta of LCC-HVDC rectifier stationαThe turn-off angle quantitative feedback quantity delta of LCC-HVDC inversion stationγ；
S23, based on the determined quantitative feedback quantity, utilizing the multi-regulation resource to inhibit the alternating current bus voltage fluctuation of the LCC-HVDC power transmission end, and realizing coordination control;
wherein the multi-regulated resources include VSC-HVDC inverter stations, LCC-HVDC rectifier stations, and LCC-HVDC inverter stations;
for the LCC-HVDC rectifying station, the trigger angle is quantitatively fed back by a control quantity deltaαThe trigger angle quantitative feedback control is realized in direct current control of the LCC-HVDC rectifier station foundation control;
for the LCC-HVDC inverter station, the turn-off angle is quantitatively fed back by a control quantity delta at the same time of triggering angle quantitative feedback controlγThe method is added to the basic control fixed-turn-off angle control of the LCC-HVDC inverter station to realize the quantitative feedback control of the turn-off angle;
in step S23, the method for quantitatively feeding back the control by using the triggering angle of the LCC rectification station specifically includes:
SB-1, action dead zone section [ delta ] for setting triggering angle quantitative feedback controlα H ,Δα L ]；
Wherein delta isα H To quantitatively feedback control the upper limit of the action, delta α L Quantitatively feeding back a control action lower limit for the trigger angle;
SB-2, LCC-HVDC rectifier station based reactive power consumptionQ dr Firing angle with LCC-HVDC rectifier stationαThe relation between the trigger angle quantitative feedback quantity delta and the trigger angle quantitative feedback quantity delta is determinedαAnd fed back to the LCC-HVDC rectification station;
SB-3, quantitative feedback quantity delta based on determined firing angleαRegulating the firing angle of a rectifier station by means of a fixed direct current through an LCC-HVDC rectifier stationαRegulating reactive power consumption of LCC-HVDC rectifier stationQ dr The quantitative feedback control of the trigger angle is realized;
in the step S23, at the start angle of the rectifying stationAnd the control method is characterized in that the turn-off angle quantitative feedback control is carried out by using the LCC-HVDC inverter station while the adjustment is carried out, and the control method specifically comprises the following steps:
SC-1, and an operation dead zone section [ delta ] for setting off angle quantitative controlγ H ，Δγ L ]；
Wherein delta isγ H For the upper limit of the action of the turn-off angle quantitative control, deltaγ L A lower limit of the action for quantitatively controlling the turn-off angle;
SC-2, LCC-HVDC inverter station based reactive powerQ di Off angle with LCC-HVDC inverter stationγDetermining the off-angle quantitative feedback control quantity delta from quantitative numerical relation of (2)γAnd fed back to the LCC-HVDC inverter station;
SC-3, quantitative feedback control quantity delta at off-angle during LCC-HVDC transmission power variationγExceeding the action dead zone interval [ delta ]γ H ，Δγ L ]When according to delta γThe LCC-HVDC inversion station adopts a mode of controlling a fixed turn-off angleγAdjusting, thereby adjusting the reactive power consumption of the LCC-HVDC rectifier stationQ dr And the quantitative feedback control of the turn-off angle is realized.
2. The method for coordinated control of feedback power of a hybrid multi-feed direct current transmission system according to claim 1, wherein in step S1, unbalanced power and ac voltage are calculatedU p The quantitative numerical relation between the two is as follows:
LCC-HVDC rectifier station consuming reactive powerQ dr Active power consumed by LCC-HVDC rectifier stationP dr Is in direct proportion to the firing angle of the rectifying stationαA cosine function relation;
when LCC-HVDC is transmittedActive power consumed by LCC-HVDC rectifier station when power transmission risesP dr Increase, inducing negative unbalanced active power, while LCC-HVDC DC currentI d Increased reactive power leading to consumption of LCC-HVDC rectifier stationQ dr The increase causes negative unbalanced reactive power, and the unbalanced reactive power and the unbalanced active power jointly cause the effective value of the alternating current bus voltage at the PCCU p Lowering;
active power consumed by an LCC rectifier station when LCC-HVDC transmission power decreasesP dr Reduced, positive unbalanced active induced, LCC-HVDC DC current simultaneouslyI d Reduction of reactive power consumed by LCC-HVDC rectifier stationQ dr Reducing, inducing positive unbalanced reactive power, wherein the unbalanced active power and the unbalanced reactive power jointly cause the effective value of the alternating current bus voltage at the PCC U p Rising.
3. The method according to claim 1, wherein in step S23, for the VSC-HVDC inverter station, the unbalanced reactive power is quantitatively fed back by an amount Δ based on the constant active power control and the constant ac voltage controlQAc bus voltage at PCCU p Is converted into a voltage feedback value to be added to a constant alternating voltage control, and unbalanced active and quantitative feedback quantity deltaPAnd the reactive power control side acts along with the action of the reactive power control side and is added to the fixed active power control to realize unbalanced power quantitative feedback control.
4. The feedback power coordination control method of the hybrid multi-feed direct current transmission system according to claim 3, wherein in the step S23, the method for performing unbalanced power quantitative feedback control by using the VSC-HVDC inverter station specifically comprises:
SA-1, and setting action dead zone section [ delta ] of unbalanced reactive power quantitative feedback controlQ H ，ΔQ L ]；
Wherein delta isQ H For unbalanced reactive power quantitative feedback control action upper limit deltaQ L The lower limit of the unbalanced reactive power quantitative feedback control action is set;
SA-2, when unbalanced reactive power quantitative feedback quantity deltaQExceeding the upper and lower limit intervals [ delta ] of the operation dead zone due to the change of LCC-HVDC transmission power Q H ，ΔQ L ]Executing an unbalanced power quantitative feedback control flow;
SA-3, reactive power quantitative feedback quantity delta of unbalanceQAc bus voltage at PCCU p The relation between the voltage feedback values is converted into voltage feedback values, the voltage feedback values are added to the VSC-HVDC inversion station, and unbalanced reactive power is further restrained through alternating current voltage of a reactive power control side of the VSC-HVDC inversion station;
SA-4, following the action of reactive power control side, will unbalance active ration feedback quantity deltaPThe variation of (2) is added to the fixed active power side to control unbalanced active power, so as to realize unbalanced power quantitative feedback control.
5. The method for coordinated control of feedback power of a hybrid multi-feed direct current transmission system according to claim 4, wherein in step SA-3, the unbalanced reactive power is quantitatively fed back by an amount ΔQAc bus voltage at PCCU p The relation between them is:
in the method, in the process of the invention,for the ac busbar voltage at PCC under normal operating conditions, +.>Equivalent impedance of AC system->Is equivalent voltage of an alternating current system.
6. The method for coordinated feedback power control of a hybrid multi-feed direct current transmission system according to claim 1, wherein in step SB-2:
LCC-HVDC rectifier station consuming reactive powerQ dr Firing angle with LCC-HVDC rectifier station αThe relation between them is:
in the method, in the process of the invention,active power consumed for LCC-HVDC rectifier station, +.>For equivalent reactance of each phase of the rectifying station, +.>For LCC-HVDC rectifier inversion side direct current, +.>The method comprises the steps of (1) obtaining an effective value of a valve side no-load line voltage of a converter transformer of a rectifying station;
quantitative feedback quantity of determined trigger angleThe method comprises the following steps:
in the method, in the process of the invention,reactive power variation is consumed for LCC-HVDC rectification during transmission power variation, +.>Active power variation for LCC-HVDC rectifier station consumption during transmission power variation, +.>For LCC-HVDC DC variation during transmission power variation, wherein +.>，/>，/>，/>For the active power consumed by the LCC-HVDC rectifier station in normal operating conditions +.>Active power consumed for LCC-HVDC rectifier station, +.>For reactive power consumed by the LCC-HVDC rectifier station in normal operating conditions +.>Reactive power consumed for LCC-HVDC rectifier station, +.>For LCC-HVDC DC under normal operating conditions, +.>Is LCC-HVDC direct current.
7. The method for coordinated feedback power control of a hybrid multi-feed direct current transmission system according to claim 1, wherein in the step SC-2, the off angle is quantitatively controlled by a feedback control amount ΔγThe method comprises the following steps:
in the method, in the process of the invention,reactive power variation for LCC-HVDC inverter station consumption during transmission power variation, +. >Active power variation for LCC-HVDC inverter station consumption during transmission power variation, +.>For the commutation reactance of an LCC-HVDC inverter station,/->For LCC-HVDC inverter station converter transformer valve side no-load line voltage effective value,/->For LCC-HVDC DC variation during transmission power variation; wherein (1)>，/>，/>Reactive power consumed by LCC-HVDC inverter station under normal operation condition +.>Reactive power for LCC-HVDC inverter station, < >>For the active power consumed by the LCC-HVDC inverter station under normal operating conditions +.>Is the active power of the LCC-HVDC inverter station.
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