CN112366968A - State space model modeling method for LCC series MMC hybrid converter station - Google Patents

State space model modeling method for LCC series MMC hybrid converter station Download PDF

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CN112366968A
CN112366968A CN202011014875.9A CN202011014875A CN112366968A CN 112366968 A CN112366968 A CN 112366968A CN 202011014875 A CN202011014875 A CN 202011014875A CN 112366968 A CN112366968 A CN 112366968A
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lcc
mmc
converter station
series
direct current
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CN112366968B (en
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郭春义
崔鹏
林欣
赵成勇
王庆华
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North China Electric Power University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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
    • 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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  • Power Engineering (AREA)
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Abstract

The invention relates to a state space model modeling method suitable for describing a coupling relation of an LCC series MMC hybrid converter station, wherein a high-voltage end LCC and a low-voltage end MMC are equivalent to a structure of voltage source series impedance on a direct current side of the converter station; respectively equating the LCC and the MMC into structures of current source series impedance and voltage source series impedance on the alternating current side of the converter station, and describing the relation between the alternating current side and the direct current side by using the switching functions of the LCC and the MMC; for the direct current side equivalent circuit, defining direct current as a common state variable of an LCC (lower control circuit) smoothing reactor and an MMC (modular multilevel converter) bridge arm reactor, and establishing a direct current side mathematical model by combining a direct current side series connection relation and a direct current mathematical model; combining the parallel relation of the alternating current sides to the equivalent circuit of the alternating current sides, and performing rotation coordinate transformation on the LCC and MMC electrical quantities at the connecting line to establish a mathematical model of the alternating current sides; and establishing the connection of the AC side and the DC side of the converter station by combining the switch functions of the LCC and the MMC to finally obtain a state space model.

Description

State space model modeling method for LCC series MMC hybrid converter station
Technical Field
The invention belongs to the technical field of power transmission and distribution, and particularly relates to a modeling method of a state space model of an LCC series MMC mixed type converter station.
Background
With the development of direct current transmission engineering towards high voltage and large capacity, the high voltage direct current conversion technology has also gained wide attention in academic and engineering fields. The hybrid direct-current transmission system integrates the advantages of the power grid commutation converter LCC and the modular multilevel converter MMC, and can reduce cost and operation loss to a certain extent. The converter station formed by connecting the LCC and the MMC in series is a mixed mode, the high-voltage end of the converter station is the LCC, the low-voltage end of the converter station is the MMC, and when the converter station runs in an inversion mode, the LCC can block a discharging path of the MMC when a direct-current fault occurs; the MMC can reduce the probability of LCC commutation failure to a certain extent; when the converter station operates as an inverter station, multi-drop point power transmission can be realized; in addition, the converter station topology is also suitable for an extra-high voltage direct current transmission system.
At present, a plurality of research achievements exist on a state space model of a direct current system aiming at LCC and MMC, but the research mainly aims at a single converter station, and the coupling relation of electric quantities of different converters in the converter station on alternating current and direct current sides is not considered; and no relevant literature report exists at home and abroad aiming at the state space model of the LCC serial MMC mixed type converter station.
Because the LCC and the MMC are directly connected in series at the direct current side and are connected in parallel at the alternating current side through a connecting line, the alternating current and direct current electrical quantity and the control quantity of the converter station have a compact and complex coupling relation, and therefore new characteristics are brought to a system dynamic model. Therefore, it is necessary to provide a state space model of the LCC serial MMC hybrid converter station, which provides a model basis for the subsequent mutual coupling analysis of the electrical quantities on the ac and dc sides of the converter station.
The invention provides a state space model modeling method of an LCC series MMC hybrid converter station. The state space model considers the coupling relation of alternating current and direct current sides among different converters in the converter station, and can accurately describe the dynamic characteristics of the LCC serial MMC hybrid converter station.
Disclosure of Invention
The invention aims to provide a state space model modeling method capable of describing the alternating current-direct current coupling relation of a multi-converter in an LCC series MMC hybrid converter station.
The adopted solution for realizing the purpose is as follows:
on the direct current side of the LCC series MMC hybrid converter station, a high-voltage end LCC and a low-voltage end MMC are equivalent to a structure of voltage source series impedance; respectively and equivalently converting the LCC and the MMC into structures of current source series impedance and voltage source series impedance on the alternating current side of the converter station;
further, for a direct current side equivalent circuit, defining direct current as a common state variable of an LCC (lower control circuit) smoothing reactor and an MMC (modular multilevel converter) bridge arm reactor, and establishing a direct current side mathematical model by combining a direct current side series relation and a direct current mathematical model;
further, combining the parallel relation of the alternating current sides to the equivalent circuit of the alternating current sides, and performing rotation coordinate transformation on the LCC and MMC electrical quantities at the connecting line to establish a mathematical model of the alternating current sides;
further, the connection of the AC side and the DC side of the converter station is established by combining the switch functions of the LCC and the MMC, and finally a state space model is obtained.
Further, the MMC converter modeling module comprises a capacitance voltage fluctuation submodule, an even number order circulation submodule and a circulation suppression control submodule.
The LCC and the MMC converter are directly connected in series on the direct current side, and the LCC and the MMC are closely connected on the direct current electrical quantity and are transferred to an alternating current system through respective switching functions; and the AC sides of the LCC and the MMC are connected in parallel through a connecting line and are transmitted back to the DC system through a switching function, so that the connection between the LCC and the MMC is tighter, namely, the electrical quantities of the LCC and the MMC are coupled on the AC side and the DC side at the same time. The state space model of the LCC serial MMC hybrid converter station considers the coupling relation of alternating current and direct current sides among different converters in the converter station, and can accurately describe the dynamic characteristics of the LCC serial MMC hybrid converter station.
Drawings
Fig. 1 is an equivalent circuit diagram of the anode of the LCC series MMC hybrid converter station.
Fig. 2 is an equivalent circuit diagram of the dc side of the LCC serial MMC hybrid converter station.
Fig. 3 is an equivalent circuit diagram of the ac side of the LCC series MMC hybrid converter station.
Fig. 4 is a comparison result of the established state space model ("SSM") and the established PSCAD electromagnetic transient model ("EMT") of the LCC series MMC hybrid converter station, the dynamic response of the system at the time of the dc voltage step of the LCC and MMC.
Detailed Description
The following describes a state space model modeling method of an LCC serial MMC hybrid converter station according to an embodiment of the present invention in detail with reference to the accompanying drawings.
As shown in fig. 1, the LCC serial MMC hybrid converter station includes a high-voltage LCC converter and a low-voltage MMC converter connected in series on the dc side and connected in parallel on the ac side via an ac interconnection line. The LCC and the MMC converter are directly connected in series on the direct current side, and the LCC and the MMC are closely connected on the direct current electrical quantity and are transferred to an alternating current system through respective switching functions; and the AC sides of the LCC and the MMC are connected in parallel through a connecting line and are transmitted back to the DC system through a switching function, so that the connection between the LCC and the MMC is tighter, namely, the electrical quantities of the LCC and the MMC are coupled on the AC side and the DC side at the same time. Based on the AC-DC side coupling relation among different converters in the LCC serial MMC hybrid converter station, the invention provides a state space model modeling method for the LCC serial MMC hybrid converter station.
When the system stably operates under the rated working condition, the direct-current voltage expression of the direct-current side LCC of the converter station is as follows:
Figure BDA0002698723370000031
in the formula of Upcc_LCCIs the LCC AC bus voltage amplitude, gamma is the turn-off angle, omegaLCCAngular frequency, L, of LCC systemst_LCCFor LCC converter transformersEquivalent inductance of the transformer, IdcIs a direct current.
The direct-current voltage expression of the direct-current side MMC of the converter station is as follows:
Figure BDA0002698723370000041
in the formula, LarmAnd RarmBridge arm inductance and equivalent loss resistance u of MMC respectivelyarm_dcThe specific expression of the direct-current component of the upper bridge arm voltage of the MMC can be solved by the switching function relation of the MMC.
As can be seen from the equations (1) and (2), the dc-side model of LCC and MMC can be equivalent to a structure of voltage source series impedance, as shown in fig. 2, in which the red line is the dc current path. As can be seen from the figure, since direct current flows through the smoothing reactor of LCC and the bridge arm reactor of MMC at the same time, I is required to be adjusteddcThe common state variable of the LCC smoothing reactor and the MMC bridge arm reactor is defined, and a mathematical model of the direct current is solved by combining the series relation of the direct current side, and the following explanation is given:
writing the KVL equation to the red line-loop column shown in fig. 2, has:
Figure BDA0002698723370000042
combining the series relation of the dc sides of the converter stations, it can be seen from fig. 1 that the voltage Ucline2And the direct current voltage U of the converter stationdcEqual, i.e.:
Ucline2＝Udc (4)
and Ucline2Is a line side capacitor C2The corresponding state variable, therefore, can be determined by the simultaneous type (1), (3), (4)dcAnd finally obtaining the direct-current voltage mathematical model of the LCC and the MMC.
When the system is stably operated under the rated working condition, the switching function describing the LCC switching process is as follows:
Figure BDA0002698723370000051
in the formula icd_LCCAnd icq_LCCIs dq component of the alternating side current of the LCC under the LCC coordinate system, beta is a leading trigger angle, gamma is an off angle,
Figure BDA0002698723370000052
is the power factor angle.
From equation (5), the LCC converter can be regarded as a current source when viewed from the AC side, and the current thereof is from the DC side IdcAnd (6) determining.
The switching function describing the MMC switching process is:
Figure BDA0002698723370000053
up(n)＝N·Sp(n)·uc (7)
in the formula (6), Sp(n)For the average switching function of the upper (lower) bridge arm, ip(n)Is the upper (lower) bridge arm current, C is the sub-module capacitance, ucIs the sub-module capacitance voltage; in the formula (7), up(n)The voltage of an upper (lower) bridge arm and N is the number of submodules. Average switching function S of bridge arm in steady state operationp(n)Comprises the following steps:
Figure BDA0002698723370000054
wherein M is a modulation ratio, alpha1And alpha2Phase angles, omega, of fundamental and frequency doubler, respectivelyMMCFor MMC system angular frequency, UcirDouble frequency correction, U, for loop suppression added to voltage-modulated wavesdcnIs an MMC dc voltage.
Neglecting quadruple frequency and higher order frequency components, obtaining MMC bridge arm current ip(n)Expression (9) and sub-module capacitance voltage ucExpression (10):
Figure BDA0002698723370000061
in the formula (I)c_MMC，β1) And (I)cir，β2) Are respectively a fundamental frequency current ic_MMCAnd a double frequency circulating current icirAmplitude and phase angle of.
uc＝Uc0+Uc1sin(ωMMCt+θ1)+Uc2sin(2ωMMCt+θ2)+Uc3sin(3ωMMCt+θ3) (10)
In the formula of Uc0Is the DC component of the capacitor voltage (U)c1，θ1)，(Uc2，θ2)，(Uc3，θ3) The amplitude and phase angle of the fundamental frequency, the frequency doubling and the frequency tripling of the capacitor voltage are respectively.
Substituting the formulas (8) and (9) into the formula (6) to obtain a mathematical model of direct current, fundamental frequency, frequency doubling and frequency tripling components of the sub-module capacitor voltage; substituting the expressions (8) and (10) into the expression (7) can obtain each frequency component of the bridge arm voltage. From this, the fundamental frequency component of MMC AC (denoted as u)arm_ac1) The expression is as follows:
Figure BDA0002698723370000062
in the formula of Uc3xAnd Uc3yIs Uc3The direct current component after passing through the fourier transform.
As can be seen from the MMC fundamental frequency voltage expression (11) derived from the MMC switching function, the MMC can be equivalent to a voltage source as shown in fig. 3 when viewed from the ac side, and an ac side mathematical model is obtained by combining the ac side system structure.
And (3) combining the LCC and MMC switching function expressions shown in the formulas (1), (6) to (7), the connection between the AC side and the DC side of the converter station can be constructed, and finally, a state space model is obtained.
Fig. 4 is a diagram showing the dynamic response ("SSM") of the state space model of the LCC series MMC hybrid converter station established at the time of the dc voltage step of the LCC and MMC in comparison with the dynamic response ("EMT") of the electromagnetic transient simulation model system of the LCC series MMC hybrid converter station in PSCAD. It can be seen from the figure that when the direct-current voltage of the LCC or the MMC is stepped, the state space model of the established LCC series MMC hybrid converter station is substantially consistent with the dynamic characteristics of the electromagnetic transient model in the PSCAD, so that the validity of the proposed state space model can be demonstrated.
The above embodiments are only used to illustrate the present invention and not to limit the technical solutions described in the present invention; thus, while the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Claims (6)

1. A state space model modeling method of an LCC series MMC hybrid converter station is characterized in that a high-voltage end LCC and a low-voltage end MMC are equivalent to a structure of voltage source series impedance on a direct current side of the converter station; respectively equating the LCC and the MMC to structures of current source series impedance and voltage source series impedance at the AC side of the converter station, describing the relation between the AC side and the DC side by using the switching functions of the LCC and the MMC, and specifically comprising the following steps:
step 1, on the direct current side of an LCC series MMC hybrid converter station, a high-voltage end LCC and a low-voltage end MMC are equivalent to a structure of voltage source series impedance; respectively and equivalently connecting the LCC and the MMC into a structure of current source series impedance and voltage source series impedance on the alternating current side of the LCC series MMC hybrid converter station;
step 2, defining the direct current as a common state variable of an LCC (lower control circuit) smoothing reactor and an MMC (modular multilevel converter) bridge arm reactor for the direct current side equivalent circuit, and establishing a direct current side mathematical model by combining a direct current side series relation and a direct current mathematical model;
step 3, combining the parallel relation of the alternating current sides of the equivalent circuit on the alternating current sides, and carrying out rotation coordinate transformation on the LCC and MMC electrical quantities at the connecting line to establish a mathematical model of the alternating current sides;
and 4, establishing the connection of the AC side and the DC side of the converter station by combining the switch functions of the LCC and the MMC, and finally obtaining a state space model.
2. The method for modeling the state space model of the LCC series MMC hybrid converter station according to claim 1, wherein: before the step 1, modeling a high-voltage end LCC and a low-voltage end MMC converter of the LCC series MMC hybrid converter station to obtain a state space model of the high-voltage end LCC and the low-voltage end MMC converter.
3. The method for modeling the state space model of the LCC series MMC hybrid converter station according to claim 2, wherein: the MMC converter modeling comprises a capacitance voltage fluctuation submodule, an even number order circulation submodule and a circulation suppression control submodule.
4. The method for modeling the state space model of the LCC series MMC hybrid converter station according to claim 1, wherein: the modeling method is used for the LCC series MMC mixed type converter station adopting the extra-high voltage class.
5. The method for modeling the state space model of the LCC series MMC hybrid converter station according to claim 1, wherein: the modeling method is used for the LCC series MMC mixed type converter station with a double-end structure.
6. The method for modeling the state space model of the LCC series MMC hybrid converter station according to claim 1, wherein: the modeling method is used for the LCC series MMC hybrid type converter station adopting a bipolar structure.
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CN115208214A (en) * 2022-07-20 2022-10-18 四川大学 LCC broadband impedance model construction method based on multi-switch function

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