CN116169705A - Multipoint direct-current voltage non-difference coordination control method for VSC-MTDC system - Google Patents

Multipoint direct-current voltage non-difference coordination control method for VSC-MTDC system Download PDF

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CN116169705A
CN116169705A CN202310041227.XA CN202310041227A CN116169705A CN 116169705 A CN116169705 A CN 116169705A CN 202310041227 A CN202310041227 A CN 202310041227A CN 116169705 A CN116169705 A CN 116169705A
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power
converter station
active power
voltage
current voltage
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李从善
和萍
刘普
张晓伟
杨小亮
王明杰
申永鹏
季玉琦
陶玉昆
赵科峰
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Zhengzhou University of Light Industry
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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
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H02J2003/365—Reducing harmonics or oscillations in HVDC
    • 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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Abstract

The invention provides a multipoint direct-current voltage difference-free coordination control method of a VSC-MTDC system, which is used for solving the technical problem of direct-current voltage deviation caused when a converter station adopts a traditional droop control method to consume unbalanced power. According to the invention, unbalanced power is reasonably distributed according to the power margin of the converter station, and the sagging curve is translated, so that the direct-current voltage can be regulated without difference; the control system collects the active power value of the non-sagging converter station and calculates the power disturbance quantity born by the sagging converter station; judging whether the power disturbance quantity is equal to 0; according to a power balance distribution method, the power disturbance quantity is used as feedforward compensation quantity, and distributed to each sagging converter station according to a power margin, and a sagging curve is translated; judging whether the direct-current voltage exceeds a set range; the control mode of the fixed active power converter station is converted into droop control, and unbalanced power adjustment is participated. The invention can realize quasi-indifferent adjustment of direct-current voltage, optimize the power flow distribution of the system and improve the running stability of the system.

Description

Multipoint direct-current voltage non-difference coordination control method for VSC-MTDC system
Technical Field
The invention relates to the technical field of droop control, in particular to a multipoint direct current voltage difference-free coordination control method of a VSC-MTDC system.
Background
With the continuous adjustment of the energy structure, the permeability of the high-capacity power electronic device in the power grid is gradually improved, and the power electronic trend is presented in the four fields of source, grid, load and storage. In the aspect of a power transmission system, a multi-terminal flexible direct current power transmission system (voltage source converter based multi-terminal high voltage direct current, VSC-MTDC) based on a voltage source converter is one of important development directions of a future long-distance power transmission technology, and gradually becomes the best choice of new energy grid connection.
Currently, inter-station control strategies applied to VSC-MTDC systems are broadly divided into three types: master-slave control, voltage margin control, and direct current droop control. The master-slave control and the voltage margin control belong to single-point control, only a single converter station participates in power regulation of a direct current system at the same time, and the dynamic response characteristic of direct current voltage is poor. The direct-current voltage sag control can utilize the power regulation capability of a plurality of converter stations to realize the rapid distribution of unbalanced power along respective sag curves, and has the advantages of good direct-current voltage response characteristic and larger direct-current voltage deviation.
Aiming at the problem of DC voltage deviation caused by droop control adopted by a converter station, students at home and abroad conduct a great deal of research, and the current control method is mainly divided into the following three control methods. The first method is to realize reasonable distribution of unbalanced power and reduce deviation of direct current voltage by improving droop coefficient. The improved droop control [ J ]. High voltage technology, 2018,44 (10): 3190-3196 ], [ Luo Yongjie, li Yaohua, wang Ping, etc. applicable to VSC-MTDC.A multi-terminal flexible DC transmission system DC voltage adaptive droop control strategy study [ J ]. Chinese motor engineering report, 2016,36 (10): 2588-2599 ], [ Liu Yingpei, descel, liang Haiping, xie Qian. Adaptive droop control of VSC-MTDC system accounting for inter-converter voltage errors [ J ]. Electrical engineering report, 2020,35 (15): 3270-3280 ], [ Zhang Yuanshi, wang Liwei and Li Wei. Autonomus DC line power flow regulation using adaptive droop control in HVDC grid [ J ]. IEEE Transactions on Power Delivery,2021,36 (6): 3550-3560 ] effectively reduces DC voltage deviation by adaptively adjusting droop coefficients. However, the deviation between the actual active power transmission value of the converter station and the reference value is continuous, and the direct-current voltage deviation is also continuous, which is unfavorable for the stable operation of the system. The second method is to achieve a indifferent regulation of the dc voltage by switching the way the converter station operates. The literature [ Yuan Zhichang, wu Zhili, jinqiang, etc. ] the VSC-MTDC interconnection system frequency stabilization control with secondary regulation of DC voltage [ J ]. Power System Automation, 2018,42 (23): 9-13+19 ] proposes to superimpose DC voltage error on the active power loop through the PI controller, and to realize the deadbeat regulation of DC voltage by utilizing the deadbeat-free characteristic of the PI controller. The document [ Zhao Xiao, shao Bingbing, han Minxiao ] provides a combined control strategy combining master-slave control and droop control for power construction 2017,38 (11): 19-25 ] based on a multi-terminal flexible direct current transmission system combined control strategy [ J ] of the N-1 rule, and the direct current voltage is regulated in a non-difference manner by a transition control mode. The documents [ Li Zhou, li Yazhou, liu Yuping, etc. ] multi-terminal flexible DC power grid active power balance coordination control strategy [ J ]. Power system automation, 2019,43 (17): 117-124 ] propose a multipoint voltage coordination control strategy, which improves the performance of DC voltage while minimizing the dynamic power deviation of the converter station. However, the essence of the control strategy described above is to change the droop control station to a constant dc voltage control station, losing the advantage of the droop control multi-station in synergy to dissipate unbalanced power. The third method is to achieve the purpose of direct current voltage indifferent adjustment by adjusting the active power reference value. The literature [ Li Zhou, li Yazhou, zhan Roupei, he Yan and Zhang xiaoping.AC grids characteristics oriented multi-point voltage coordinated control strategy for VSC-MTDC [ J ]. IEEE Access,2019,7:7728-7736 ] is superimposed on the active power loop by harvesting the unbalanced power of the DC system, realizing the translation of the sagging curve. The literature [ Liuyu, liu Chongru, zheng Le, wang Qunqiao ] discloses a VSC-MTDC system with quasi-dc correction to cooperatively optimize droop control [ J ]. Power system automation, 2022,46 (06): 117-126 ] proves that after the dc system is subjected to power disturbance, each converter station can not restore the dc voltage to a rated value while maintaining the output power unchanged, and further proposes a coordinated control strategy with minimum power change and minimum dc voltage deviation of the converter station, so as to realize "pseudo" non-differential regulation of the dc voltage. However, the dc voltage deviation is also relatively large.
Disclosure of Invention
Aiming at the technical problem of direct-current voltage deviation caused when the traditional droop control method is adopted by a converter station to consume unbalanced power, the invention provides the multipoint direct-current voltage difference-free coordination control method of the VSC-MTDC system, which can realize the quasi-difference adjustment of the direct-current voltage, optimize the power flow distribution of the system and improve the running stability of the system.
In order to achieve the above purpose, the technical scheme of the invention is realized as follows: a multipoint direct-current voltage non-difference coordination control method of a VSC-MTDC system reasonably distributes unbalanced power according to a power margin of a converter station, translates a droop curve and realizes non-difference adjustment of direct-current voltage; the method comprises the following steps:
step one, a control system collects active power values of a non-sagging converter station at a moment t and a moment t+delta t, and calculates a power disturbance quantity delta P born by an ith sagging converter station;
step two, judging whether the power disturbance quantity delta P is equal to 0, if so, returning to the step one, otherwise, entering the step three;
step three, according to a power balance distribution method, the power disturbance quantity delta P is used as a feedforward compensation quantity, and is distributed to each sagging converter station according to a power margin, and the quasi-non-difference adjustment of the direct-current voltage is realized by translating a sagging curve;
judging whether the direct-current voltage exceeds a set range, if not, returning to the first step, and if so, entering a fifth step;
and fifthly, converting a control mode of the fixed active power converter station into droop control to participate in unbalanced power regulation.
Preferably, the control system comprises a multi-purpose meter, a data transmission module and a calculation module, wherein the multi-purpose meter is connected with the data transmission module, the data transmission module is connected with the calculation module, the multi-purpose meter collects the active power value of the non-sagging converter station, and the active power value is sent to the calculation module through the data transmission module.
Preferably, the method for calculating the power disturbance quantity Δp is as follows:
the direct current voltages of all the converter stations are equal;
under steady state conditions, the relationship between the direct current voltage of the converter station and the active power is: u (U) dc ＝U dcref +k(P s -P sref ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein U is dc And U dcref Respectively representing the measured voltage value and the voltage reference value of the direct current side, k is the sagging coefficient, and P s And P sref Representing an actual active power measured value and an active power reference value of the converter station respectively;
setting a VSC-MTDC system with N converter stations, wherein 1-m converter stations adopt traditional droop control to consume unbalanced power in the VSC-MTDC system and stabilize direct current voltage; m+1 to N converter stations are controlled by fixed active power, and n+1 to N converter stations are controlled by fixed alternating voltage;
1-m sum of active power reference values of sagging converter stations
Figure BDA0004050734250000031
Wherein P is i An active power reference value of the ith sagging converter station is equal to or more than 1 and equal to or less than m; />
Sum of m+1 to n fixed active power converter station power reference values
Figure BDA0004050734250000032
Wherein P is b An active power reference value of an active power converter station is determined for the b-th active power converter station, and m+1 is more than or equal to b and less than or equal to n;
sum of n+1 to N active power transmission values of constant AC voltage converter station
Figure BDA0004050734250000033
Wherein P is j The active power transmission value of the jth constant alternating voltage converter station is n+1 which is not less than j which is not more than N;
when the power disturbance delta P occurs in the direct current system in the initial steady state, m-1 converter stations utilize the self-sagging characteristic to absorb unbalanced power of the network, and meanwhile, a steady operation point moves along with the unbalanced power; when the VSC-MTDC system reaches steady state again, the i-th droop converter station assumes an unbalanced power Δp i Deviation from DC voltage DeltaU dc The relation of (2) is that
Figure BDA0004050734250000034
The sum of the active power variations of the respective sagging converter stations is equal to the power disturbance quantity deltap, i.e.>
Figure BDA0004050734250000035
Thus, the first and second substrates are bonded together,
Figure BDA0004050734250000036
DC voltage deviation DeltaU dc Proportional to the power disturbance ΔP, and to the droop coefficient k of m droop converter stations i The sum of the reciprocals is inversely proportional; sag coefficient k i The amount of unbalanced power that the converter station assumes during dynamic regulation is determined.
Preferably, the direct current voltage is regulated without difference by reasonably distributing the unbalanced power of the direct current system and injecting the unbalanced power to the active power reference value of the converter station.
Preferably, at initial steady state, when the DC system is disturbed by unbalanced power, a feedforward compensation amount is given to each droop converter station, the magnitude of which is the unbalanced power DeltaP i The method comprises the steps of carrying out a first treatment on the surface of the At the moment, the stable operating point of the VSC-MTDC system is changed from the initial stable operating point to the operating point instantaneously reached by the system under the feedforward compensation power, so that the translation of a sagging curve is realized, and P is satisfied i ＝P isref -ΔP i The method comprises the steps of carrying out a first treatment on the surface of the Wherein P is isref And P i "active power reference values before and after adjustment for the ith droop converter station, respectively;
the droop convertor station absorbs unbalanced power according to droop characteristics, the VSC-MTDC system stably operates near a stable operation point of recovering to rated voltage under the condition of not changing output power, and the direct-current voltage is regulated without difference.
Preferably, in order to reasonably distribute the unbalanced power in the direct current system to the respective sagging converter stations, the available power margin of the sagging converter stations is introduced to the power distribution coefficient, and the active power reference value is quickly adjusted.
Preferably, the implementation method for introducing the available power margin of the drooping converter station onto the power distribution coefficient is as follows:
Figure BDA0004050734250000041
wherein P is isref ' is the active power reference value of the ith sagging converter station after optimization; p (P) t (t+Δt)、P w (t+Δt) represents the active power transmission values of the fixed active power converter station and the fixed ac voltage control converter station at time t+Δt, P t (t)、P w (t) representing the active power transfer values of the fixed active power converter station and the fixed ac voltage controlled converter station, respectively, at time t; Δt is the sampling time.
Preferably, the set range is set in accordance with the available power margin of the droop converter station in the VSC-MTDC system used.
Preferably, direct voltage deviation control is introduced into the fixed active power converter station when the direct voltage exceeds (U dc l ，U dc h ) When the operation range is reached, the conversion control mode of the fixed active power converter station is droop control, and the fixed active power converter station is cooperated with the droop converter station to consume the rest unbalanced power in the system to bear the task of stabilizing the direct current voltage; wherein U is dc l 、U dc h Respectively representing a lower limit value and an upper limit value of the set range; the DC voltage deviation droop coefficient is
Figure BDA0004050734250000042
Wherein k is b Is the droop coefficient of DC voltage deviation, P bmax Determining the maximum capacity of the active power converter station; p (P) b The active power of the active power converter station is determined for the b-th.
The coordinated control method of multipoint direct current voltage no difference in a VSC-MTDC system according to claim 9, wherein the fixed active power converter station adopts direct current voltage deviation droop control, and after the droop converter station loses the capability of controlling direct current voltage, the remaining unbalanced power in the VSC-MTDC system is set as Δp * The method comprises the steps of carrying out a first treatment on the surface of the When the VSC-MTDC system reaches balance again, the active power of the direct-current voltage deviation droop converter station is as follows
Figure BDA0004050734250000043
Wherein P is j ' active power, k of converter station controlled by deviation after system stabilization b Droop coefficient, P, for the b-th fixed active power converter station b An active power reference value for the active power converter station is determined for the b-th.
The invention has the beneficial effects that: injecting unbalanced power as feedforward compensation quantity into traditional droop control, and realizing quasi-deadening adjustment of direct-current voltage by translating a droop curve; reasonably setting feedforward compensation quantity of each converter station according to the power margin of the converter station; in order to avoid the situation that the unbalanced power is too large to cause the drooping control converter station to run in full load, deviation control is introduced into the fixed active power converter station, and the drooping control converter station is cooperated to consume the rest unbalanced power; and finally, establishing a five-terminal VSC-MTDC system based on PSCAD/EMTDC for simulation. Simulation results show that the invention can realize quasi-deadbeat regulation of direct-current voltage, optimize the power flow distribution of the system and improve the operation stability of the VSC-MTDC system. According to the invention, unbalanced power of the power margin distribution system of the converter station can be effectively avoided from being overloaded in part of the converter stations and the other converter stations still have power margins; the feedforward compensation active power reference value is adopted to translate the sagging curve, so that the direct-current voltage can be regulated approximately; by introducing a droop control to the fixed active power converter station, system operational stability when the unbalanced power is excessive or the converter station is out of operation is improved.
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In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the present invention.
Fig. 2 is a block diagram of a VSC-MTDC system.
Fig. 3 shows characteristics of the dc voltage droop control in the conventional droop control, in which (a) is the dc side converter station VSC1 and (b) is the dc side converter station VSC2.
Fig. 4 is a schematic diagram of a dc voltage droop controller.
Fig. 5 shows characteristics of the optimal coordinated control strategy according to the present invention, wherein (a) is the dc side converter station VSC1 and (b) is the dc side converter station VSC2.
Fig. 6 is a control characteristic of the VSC-MTDC system of the present invention.
Fig. 7 shows the power increase simulation results of the VSC-MTDC system, wherein (a) is the active power of the converter station VSC1, (b) is the active power of the converter station VSC2, (c) is the active power of the converter stations VSC3, VSC4, VSC5, and (d) is the system dc voltage.
Fig. 8 shows the power reduction simulation results of the VSC-MTDC system, wherein (a) is the active power of the converter station VSC1, (b) is the active power of the converter station VSC2, (c) is the active power of the converter stations VSC3, VSC4, VSC5, and (d) is the system dc voltage.
Fig. 9 shows simulation results of the exit of the converter station according to the present invention, wherein (a) is active power of the converter stations VSC1, VSC2, VSC5, (b) is active power of the converter station VSC3, (c) is active power of the converter station VSC4, and (d) is system dc voltage.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the multipoint direct current voltage no-difference coordination control method of the VSC-MTDC system is a new optimization coordination control strategy, unbalanced power is reasonably distributed according to the power margin of a converter station, and a sagging curve is translated, so that no-difference adjustment of the direct current voltage is approximately realized. Meanwhile, the deviation droop control is introduced into the fixed active power converter station, so that the droop station is prevented from being fully loaded and losing the capability of controlling the direct current voltage. Finally, the PSCAD/EMTDC five-end VSC-MTDC system is used for simulation, and the effectiveness of the provided control strategy is verified through simulation results. The method comprises the following specific steps:
step one, the control system collects active power values of the non-sagging converter stations at the time t and the time t+delta t, and calculates the power disturbance quantity delta P born by the ith sagging converter station.
The five-terminal VSC-MTDC system structure is shown in fig. 2, where VSC1 to VSC5 respectively represent five voltage source type converter stations, the converter stations VSC1 and VSC2 on the dc side are connected in parallel through a dc network, and the converter stations VSC3 to VSC5 on the ac side are connected to respective ac power grids. The direct current side is directly connected with the alternating current side.
By analogy with the primary frequency modulation characteristic of the traditional generator, the sagging control does not need inter-station communication, and the characteristic curve between the direct current voltage and the active power is utilized to realize the controlNow a fast distribution of unbalanced power and a stable control of the dc voltage. DC voltage-active power (U) dc -P s ) The control characteristics and controller configuration are shown in fig. 3 and 4, respectively. In fig. 3 and 4, U dc And U dcref Respectively represent the measured value and the reference value of the DC side voltage, P s 、P isref And P imax Representing the real power measured value, the reference value and the rated capacity value of the converter station respectively, k is a droop coefficient, i=1, 2, and represents the droop converter stations VSC1 and VSC2.U (U) dc ' direct-current voltage value delta U of system after unbalanced power is absorbed by convertor station dc Delta P is the system DC voltage variation 1 、ΔP 2 Active power variation amounts of converter stations VSC1 and VSC2, respectively, a 1 、A 2 Initial stable operating points, B, for converter stations VSC1 and VSC2, respectively 1 、B 2 The state points of stable operation are reached again after unbalance power is absorbed by the converter stations VSC1 and VSC2 respectively, C 1 、C 2 Representing stable operating points at which the converter stations VSC1 and VSC2, respectively, return to rated voltage without changing the output power. To simplify the analysis, the present invention considers the dc voltages of all converter stations to be equal.
In steady state conditions, the relationship between dc voltage and active power of the converter station can be obtained from fig. 3 as:
U dc ＝U dcref +k(P s -P sref )(1)
assuming that the direct current system has N converter stations, wherein 1-m converter stations adopt the traditional droop control to consume unbalanced power in the VSC-MTDC system and stabilize direct current voltage; the m+1 to N converter stations are controlled by fixed active power, and the n+1 to N converter stations are controlled by fixed alternating voltage. The fixed active power control can meet the requirements of an alternating current system on stable and high-quality active power input, and the fixed alternating current voltage control can provide stable alternating current voltage support for a new energy station while absorbing fluctuating active power.
Sum P of active power reference values of 1-m sagging converter stations r Is that
Figure BDA0004050734250000071
Wherein P is i And the active power reference value of the ith sagging converter station is equal to or more than 1 and equal to or less than m.
Sum P of m+1-n fixed active power converter station power reference values t Is that
Figure BDA0004050734250000072
Wherein P is b And (3) setting an active power reference value of the active power converter station for the b-th active power converter station, wherein m+1 is more than or equal to b and less than or equal to n.
Sum P of n+1 to N active power transmission values of constant AC voltage converter station w Is that
Figure BDA0004050734250000073
Wherein P is j And the active power transmission value of the jth constant alternating voltage converter station is n+1 which is not less than j and not more than N.
When the system is in an initial steady state, the system operates in a state 1, and when the power disturbance delta P occurs in the direct current system, the m-1 converter stations utilize the droop characteristic of the converter stations to absorb unbalanced power of the network, and meanwhile, the steady operation point also moves along with the unbalanced power. When the VSC-MTDC system reaches steady state again, the system operates in a state 2, and the DC voltage deviation is set as delta U dc As can be seen from FIG. 3, the droop converter station i (1. Ltoreq.i.ltoreq.m) assumes an unbalanced power ΔP i Deviation from DC voltage DeltaU dc There is the following relationship
Figure BDA0004050734250000074
The sum of the active power variation of each sagging station is equal to the power disturbance delta P, i.e. according to the energy conservation
Figure BDA0004050734250000075
Combining the formula (4) with the formula (5) to obtain
Figure BDA0004050734250000076
Figure BDA0004050734250000077
From equation (6), it can be seen that the DC voltage deviation DeltaU dc Proportional to the amount of power disturbance ΔP and inversely proportional to the sum of the reciprocal droop coefficients of m-1 droop stations. This means that when the power of the dc system fluctuates, all the converter stations cooperatively consume unbalanced power according to their sagging curves, however, the associated dc voltage deviation affects the normal operation of the system.
It can be seen from equation (7) that the droop factor determines how much of the unbalanced power the converter station is subjected to during dynamic regulation. If the converter stations use the same droop coefficient, all the converter stations equally divide the unbalanced power. If each converter station adopts different droop coefficients, the converter station with smaller droop coefficient will bear more unbalanced power, and the converter station with larger droop number will bear less unbalanced power.
The control system mainly comprises a multi-purpose table, a data transmission module and a calculation module in PSCAD software. The active power value of the non-sagging converter station is collected mainly by a multimeter and is sent to a calculation module through a data transmission module. The power disturbance quantity is generally generated on the non-sagging converter station, so that the power disturbance quantity can be obtained by acquiring the difference between the active power values of the non-sagging converter station twice in one sampling period.
And step two, judging whether the power disturbance quantity delta P is equal to 0, if so, returning to the step one, otherwise, entering the step three.
The unbalanced power is mainly caused by the power fluctuation of the new energy station, and the power fluctuation of the new energy station is replaced by the power fluctuation of the fixed active power converter station. The invention aims to recover the direct current voltage to about the rated value through an additional control strategy after the converter station is subjected to power disturbance, thereby realizing the quasi-indifferent adjustment of the direct current voltage, and obtaining the accurate value of the power disturbance quantity.
And thirdly, according to a power balance distribution method, the power disturbance quantity delta P is used as a feedforward compensation quantity, and is distributed to each sagging converter station according to a power margin, and the quasi-non-difference adjustment of the direct-current voltage is realized by translating a sagging curve.
Aiming at the problem that the direct current voltage deviation is larger due to the fact that the traditional droop control is adopted by the converter station, the invention provides a multi-droop-station cooperative optimization control strategy capable of approximately realizing direct current voltage indifferent adjustment.
The characteristic curve of the optimal coordinated control strategy is shown in fig. 5. Wherein U is dc "is the dc voltage of the converter station at the feedforward compensation power; p (P) 1 ”、P 2 "active power values of converter stations VSC1 and VSC2, respectively, at feedforward compensation power; d (D) 1 、D 2 The operating points reached by the converter stations VSC1 and VSC2, respectively, instantaneously by the system at the feed-forward compensation power.
At the initial steady state, the system operates in state 1, and when the direct current system is disturbed by unbalanced power, a feedforward compensation amount with the delta P is given to each sagging station i . At the moment, the stable operation point of the system is from A i Become D i Realize the translation of the sagging curve, P isref And P i "respectively adjusting the active power reference values before and after the converter station, satisfies the following conditions
P i ＝P isref -ΔP i (8)
And then the converter station absorbs unbalanced power according to the sagging characteristic, and finally the system stably operates at C i Near the point, a indifferent regulation of the direct voltage is approximately achieved. Compared with the traditional direct-current voltage sagging, the active power transmitted by the converter station is not changed, the direct-current voltage deviation is approximately zero, and the stability of the system is greatly improvedHigh.
In order to reasonably distribute unbalanced power in a direct current system to each sagging station, the invention introduces the available power margin of the converter station to a power distribution coefficient and quickly adjusts an active power reference value. The specific method comprises the following steps of
Figure BDA0004050734250000091
Wherein P is isref ' is the optimized droop converter station active power reference. P (P) t (t+Δt)、P w (t+Δt) represents the active power transmission values of the fixed active power converter station and the fixed ac voltage control converter station at time t+Δt, P t (t)、P w (t) representing the active power transfer values of the fixed active power converter station and the fixed ac voltage controlled converter station, respectively, at time t; Δt is the system sampling time.
Under the power distribution strategy, the control system only needs to collect the active power value of the non-sagging converter station, and updates the active power reference value to the sagging station if and only if the power flow of the direct current system changes. According to equation (9), if the active power transmission value of the non-sagging station is not changed during the sampling time, the numerator of the equation is 0, and thus the active power reference value of the sagging station is not changed. In other cases, the droop converter station only needs to operate stably according to the last updated active power reference value. The power distribution strategy has extremely low requirements on inter-station communication, and because the power distribution strategy needs an active power transmission value of a non-sagging station, the power distribution strategy needs to transmit through a communication data channel in actual engineering, does not increase the burden of a communication system, and has low requirements on communication. Even when the communication of each converter station is interrupted, the droop station can still normally operate according to the traditional droop control mode. Even when the communication of each converter station is interrupted, the sagging converter stations can still normally operate according to the conventional sagging control manner.
And step four, judging whether the direct-current voltage exceeds a set range, if not, returning to the step one, and if yes, entering the step five.
The direct-current voltage deviation droop control provided by the invention is to judge whether the direct-current voltage exceeds a set operation range so as to change the control mode of the fixed active power converter station into droop control. The set range is set according to the available power margin of the droop station in the five-end model used.
And fifthly, converting a control mode of the fixed active power converter station into droop control to participate in unbalanced power regulation.
When the coordination control strategy is adopted, if faults such as overlarge unbalanced power of a system or withdrawal of a converter station are encountered, the faults exceed the adjustment range of all the drooping converter stations, and the drooping converter stations are fully loaded and converted into fixed active power operation to lose the capability of controlling direct current voltage. In order to avoid the occurrence of the above situation, the invention introduces DC voltage deviation control into the fixed active power converter station when the DC voltage exceeds (U dc l ，U dc h ) U during operation range dc l 、U dc h The lower limit value and the upper limit value of the set range are respectively indicated. The conversion control mode of the active power converter station is droop control, and the active power converter station is cooperated with the droop converter station to consume the rest unbalanced power in the system and bears the task of stabilizing the direct current voltage. The DC voltage deviation droop coefficient is set as
Figure BDA0004050734250000092
Wherein k is b Is the droop coefficient of DC voltage deviation, P bmax The maximum capacity of the active power converter station is defined. P (P) b The active power of the active power converter station is determined for the b-th. U (U) dcl Indicating the set lower limit of the dc voltage operating range.
The active power-fixed converter station adopts direct-current voltage deviation droop control, and after the droop converter station loses the capability of controlling direct-current voltage, the residual unbalanced power in the direct-current system is set as delta P * . When the VSC-MTDC system reaches balance again, the active power of the direct-current voltage deviation droop converter station is as follows
Figure BDA0004050734250000101
Wherein P is j ' the active power of the converter station is controlled by adopting deviation after the system is stabilized.
For the five-terminal VSC-MTDC system shown in fig. 2, VSC1 and VSC2 employ optimized droop control, VSC3 and VSC4 employ dc voltage deviation droop control, and VSC5 employs constant ac voltage control. The VSC-MTDC system control characteristic is shown in fig. 6. As can be seen from fig. 6, when the dc voltage exceeds the set range, the converter station VSC3 and the converter station VSC4 will change the control mode to droop control, and the original droop stations are cooperated to absorb the unbalanced power in the system, so as to improve the stability of the system.
The invention builds a five-end VSC-MTDC system shown in figure 2 in PSCAD/EMTDC, and specific simulation parameters are shown in table 1. And comparing three control strategies through three simulation examples, and verifying the validity of the provided control strategy.
Control strategy 1 (CM 1): conventional droop control;
control strategy 2 (CM 2): optimizing coordination control;
control strategy 3 (CM 3): optimization coordination control and deviation droop control.
TABLE 1 simulation parameters of VSC-MTDC System
Figure BDA0004050734250000102
At t=3s, the active power command value of the converter station VSC3 increases from 115MW to 185MW, and the simulation result is shown in fig. 7. As can be seen from fig. 7, the active power of the converter station, the system dc voltage and the nominal value differ slightly due to losses in the VSC-MTDC system. Let DeltaP be 1 -ΔP 5 Delta U for active power variation of converter stations VSC1-VSC5 dc Is the DC voltage deviation. When t=3s, the dc system has surplus power, under the action of the control strategy CM1, the converter stations VSC1 and VSC2 consume unbalanced power according to the conventional droop control, and when the dc system reaches againAt steady state, ΔP 1 And DeltaP 2 23.5MW and 46.5MW, respectively, DC voltage deviation DeltaU dc 7.09kV and a deviation of 1.77%. Under the control strategy CM2, ΔP 1 And DeltaP 2 Respectively 16MW and 54MW, DC voltage deviation delta U dc The deviation rate is 0.035% and 0.14kV, and the direct-current voltage is corrected approximately without difference. Meanwhile, the system distributes more unbalanced power to the converter stations with larger power margin, so that the unbalanced power borne by the converter station VSC2 is more than that borne by the converter station VSC1, and the converter station VSC1 with smaller power margin is prevented from being fully loaded. The dc voltage does not exceed the running range set by the system, so the simulation result under the control strategy CM3 is the same as that under the control strategy CM 2.
At t=3s, the active power command value of the converter station VSC3 decreases from 115MW to 45MW, and the simulation result is shown in fig. 8. At t=3s, the dc system suffers from power defect, as can be seen from fig. 8, Δp under the control strategy CM1 1 And DeltaP 2 23.5MW and 46.5MW, respectively, DC voltage deviation DeltaU dc The deviation was 7.03kV and 1.76%. Δp under the control strategy CM2 or CM3 1 And DeltaP 2 42MW and 28MW, respectively, DC voltage deviation DeltaU dc The deviation was 0.028% at 0.11 kV. At this time, the power margin of the converter station VSC1 is greater than that of the converter station VSC2, so the converter station VSC1 assumes more unbalanced power than the converter station VSC2.
At t=3s, the converter station VSC2 exits operation and the simulation results are shown in fig. 9. As can be seen from fig. 9, under the control strategy CM1, the converter station VSC1 acts as the only power balance point, reaches full load soon and switches to active power operation, losing the ability to control the dc voltage, which will continue to drop. Under the action of the control strategy CM2, since the control modes of the converter station VSC3 and the converter station VSC4 are still fixed active power and do not participate in the regulation of power, Δp is calculated 2 And DeltaP 3 Are all 0. Under the action of the control strategy CM3, when the direct current voltage drops to 390kV, the converter station VSC3 and the converter station VSC4 are converted from fixed active power to droop control, and the unbalanced power is consumed by the cooperative converter station VSC1 to bear the task of stabilizing the direct current voltage.After the DC system enters steady state, ΔP 1 、ΔP 3 And DeltaP 4 26MW, 41MW and 33MW, respectively, DC voltage deviation DeltaU dc 14.49kV and a deviation of 3.62%. Meanwhile, the converter station VSC1 does not reach full load, and has the capability of stabilizing direct current voltage, so that the stability of the system is greatly improved.
From the above simulation, it can be seen that: when the converter station adopts the traditional droop control, the DC voltage deviation is larger after being disturbed by unbalanced power; when the power control strategy of the invention is adopted, the DC voltage deviation is approximately zero, and the quasi-indifferent adjustment of the DC voltage is realized.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims (10)

1. A multipoint direct current voltage non-difference coordination control method of a VSC-MTDC system is characterized in that unbalanced power is reasonably distributed according to a power margin of a converter station, a sagging curve is translated, and non-difference adjustment of direct current voltage is achieved; the method comprises the following steps:
step one, a control system collects active power values of a non-sagging converter station at a moment t and a moment t+delta t, and calculates a power disturbance quantity delta P born by an ith sagging converter station;
step two, judging whether the power disturbance quantity delta P is equal to 0, if so, returning to the step one, otherwise, entering the step three;
step three, according to a power balance distribution method, the power disturbance quantity delta P is used as a feedforward compensation quantity, and is distributed to each sagging converter station according to a power margin, and the quasi-non-difference adjustment of the direct-current voltage is realized by translating a sagging curve;
judging whether the direct-current voltage exceeds a set range, if not, returning to the first step, and if so, entering a fifth step;
and fifthly, converting a control mode of the fixed active power converter station into droop control to participate in unbalanced power regulation.
2. The multipoint direct current voltage difference-free coordination control method of the VSC-MTDC system according to claim 1, wherein the control system comprises a multimeter, a data transmission module and a calculation module, the multimeter is connected with the data transmission module, the data transmission module is connected with the calculation module, the multimeter collects active power values of the non-sagging converter stations, and the active power values are sent to the calculation module through the data transmission module.
3. The multipoint direct current voltage no-difference coordination control method of the VSC-MTDC system according to claim 1 or 2, wherein the calculating method of the power disturbance quantity Δp is as follows:
the direct current voltages of all the converter stations are equal;
under steady state conditions, the relationship between the direct current voltage of the converter station and the active power is: u (U) dc ＝U dcref +k(P s -P sref ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein U is dc And U dcref Respectively representing the measured voltage value and the voltage reference value of the direct current side, k is the sagging coefficient, and P s And P sref Representing an actual active power measured value and an active power reference value of the converter station respectively;
setting a VSC-MTDC system with N converter stations, wherein 1-m converter stations adopt traditional droop control to consume unbalanced power in the VSC-MTDC system and stabilize direct current voltage; m+1 to N converter stations are controlled by fixed active power, and n+1 to N converter stations are controlled by fixed alternating voltage;
1-m sum of active power reference values of sagging converter stations
Figure FDA0004050734240000011
Wherein P is i An active power reference value of the ith sagging converter station is equal to or more than 1 and equal to or less than m;
sum of m+1 to n fixed active power converter station power reference values
Figure FDA0004050734240000012
Wherein P is b Active power converter station for b-thAn active power reference value, m+1 is more than or equal to b and less than or equal to n;
sum of n+1 to N active power transmission values of constant AC voltage converter station
Figure FDA0004050734240000013
Wherein P is j The active power transmission value of the jth constant alternating voltage converter station is n+1 which is not less than j which is not more than N;
when the power disturbance delta P occurs in the direct current system in the initial steady state, m-1 converter stations utilize the self-sagging characteristic to absorb unbalanced power of the network, and meanwhile, a steady operation point moves along with the unbalanced power; when the VSC-MTDC system reaches steady state again, the i-th droop converter station assumes an unbalanced power Δp i Deviation from DC voltage DeltaU dc The relation of (2) is that
Figure FDA0004050734240000021
The sum of the active power variations of the respective sagging converter stations is equal to the power disturbance quantity deltap, i.e.>
Figure FDA0004050734240000022
/>
Thus, the first and second substrates are bonded together,
Figure FDA0004050734240000023
DC voltage deviation DeltaU dc Proportional to the power disturbance ΔP, and to the droop coefficient k of m droop converter stations i The sum of the reciprocals is inversely proportional; sag coefficient k i The amount of unbalanced power that the converter station assumes during dynamic regulation is determined.
4. A multipoint direct current voltage non-difference coordination control method according to claim 3, wherein the non-difference adjustment of the direct current voltage is realized by reasonably distributing unbalanced power of the direct current system and injecting the unbalanced power to an active power reference value of a converter station.
5. The method of coordinated control of multipoint direct current voltage no difference in VSC-MTDC system according to claim 4, wherein at initial steady state, when the direct current system is disturbed by unbalanced power, a feedforward compensation amount is given to each sagging converter station, the magnitude of which is the unbalanced power Δp i The method comprises the steps of carrying out a first treatment on the surface of the At the moment, the stable operating point of the VSC-MTDC system is changed from the initial stable operating point to the operating point instantaneously reached by the system under the feedforward compensation power, so that the translation of a sagging curve is realized, and P is satisfied i ＝P isref -ΔP i The method comprises the steps of carrying out a first treatment on the surface of the Wherein P is isref And P i "active power reference values before and after adjustment for the ith droop converter station, respectively;
the droop convertor station absorbs unbalanced power according to droop characteristics, the VSC-MTDC system stably operates near a stable operation point of recovering to rated voltage under the condition of not changing output power, and the direct-current voltage is regulated without difference.
6. The multipoint direct current voltage no-difference coordination control method of the VSC-MTDC system according to claim 5, wherein the reasonable allocation of the unbalanced power in the direct current system to each sagging converter station is to introduce the available power margin of the sagging converter station to the power allocation coefficient, and rapidly adjust the active power reference value.
7. The multipoint direct current voltage no-difference coordination control method of the VSC-MTDC system according to claim 1, wherein the implementation method for introducing the available power margin of the droop converter station onto the power distribution coefficient is as follows:
Figure FDA0004050734240000024
wherein P is isref ' is the active power reference value of the ith sagging converter station after optimization; p (P) t (t+Δt)、P w (t+Δt) represents the active power transmission values of the fixed active power converter station and the fixed ac voltage control converter station at time t+Δt, P t (t)、P w (t) represents the fixed active power at time t respectivelyThe power converter station and the fixed alternating current voltage control the active power transmission value of the converter station; Δt is the sampling time.
8. A VSC-MTDC system multipoint direct voltage difference free coordination control method according to any one of claims 4-7, characterized in that the setting range is set according to the available power margin of the sagging converter station in the VSC-MTDC system used.
9. The method of coordinated control of the multipoint direct voltage difference of a VSC-MTDC system according to claim 8, characterized in that the direct voltage deviation control is introduced into the fixed active power converter station when the direct voltage exceeds (U dc l ，U dc h ) When the operation range is reached, the conversion control mode of the fixed active power converter station is droop control, and the fixed active power converter station is cooperated with the droop converter station to consume the rest unbalanced power in the system to bear the task of stabilizing the direct current voltage; wherein U is dc l 、U dc h Respectively representing a lower limit value and an upper limit value of the set range; the DC voltage deviation droop coefficient is
Figure FDA0004050734240000031
Wherein k is b Is the droop coefficient of DC voltage deviation, P bmax Determining the maximum capacity of the active power converter station; p (P) b The active power of the active power converter station is determined for the b-th.
10. The coordinated control method of multipoint direct current voltage no difference in a VSC-MTDC system according to claim 9, wherein the fixed active power converter station adopts direct current voltage deviation droop control, and after the droop converter station loses the capability of controlling direct current voltage, the remaining unbalanced power in the VSC-MTDC system is set as Δp * The method comprises the steps of carrying out a first treatment on the surface of the When the VSC-MTDC system reaches balance again, the active power of the direct-current voltage deviation droop converter station is as follows
Figure FDA0004050734240000032
Wherein P is j ' active power, k of converter station controlled by deviation after system stabilization b Droop coefficient, P, for the b-th fixed active power converter station b An active power reference value for the active power converter station is determined for the b-th. />
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116845926A (en) * 2023-08-28 2023-10-03 广东电网有限责任公司珠海供电局 Multi-port power coordination control method and related device
CN117239817A (en) * 2023-09-20 2023-12-15 兰州理工大学 Light storage and wind-solar coordination operation method based on flexible direct current grid connection

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116845926A (en) * 2023-08-28 2023-10-03 广东电网有限责任公司珠海供电局 Multi-port power coordination control method and related device
CN116845926B (en) * 2023-08-28 2024-01-19 广东电网有限责任公司珠海供电局 Multi-port power coordination control method and related device
CN117239817A (en) * 2023-09-20 2023-12-15 兰州理工大学 Light storage and wind-solar coordination operation method based on flexible direct current grid connection
CN117239817B (en) * 2023-09-20 2024-05-03 兰州理工大学 Light storage and wind-solar coordination operation method based on flexible direct current grid connection

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