CN108258891B - Method and device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations - Google Patents

Method and device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations Download PDF

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CN108258891B
CN108258891B CN201611234824.0A CN201611234824A CN108258891B CN 108258891 B CN108258891 B CN 108258891B CN 201611234824 A CN201611234824 A CN 201611234824A CN 108258891 B CN108258891 B CN 108258891B
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mmc
direct current
virtual resistor
hvdc
virtual
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CN108258891A (en
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吴广禄
彭红英
张星
徐得超
穆清
陈绪江
孙丽香
刘敏
王峰
林因
吴丹岳
黄道姗
黄霆
刘智煖
苏清梅
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
Electric Power Research Institute of State Grid Fujian Electric Power Co Ltd
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
Electric Power Research Institute of State Grid Fujian Electric Power Co Ltd
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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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H02J2003/365—Reducing harmonics or oscillations in HVDC
    • 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 method and a device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations, wherein the method comprises the following steps: extracting direct current fluctuation components from direct current, and determining the resistance value of a virtual resistor introduced from the MMC-HVDC direct current side; determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor; and determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor. The invention can inhibit the generation of MMC-HVDC direct current side current resonance under the condition of not increasing extra loss, and reduce the possibility of the generation of MMC-HVDC direct current side fault, thereby improving the utilization efficiency of the voltage source converter and saving the cost; because the equivalent position of the virtual resistor is on the bridge arm, the resonance in the station is also inhibited; the method is mainly realized by improving the upper control of the MMC, and is easy to implement.

Description

Method and device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a method and a device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations.
Background
Although MMC-HVDC (Modular Multilevel Converter) based Direct Current Transmission takes resonance characteristics in and among MMC-HVDC stations into consideration during main circuit parameter design, the possibility of resonance of MMC-HVDC at fundamental frequency and characteristic subharmonic frequency is avoided in main circuit parameter selection, but an equivalent resistance, capacitance and inductance series loop at the Direct Current side still has inherent resonance frequency, so that resonance is possible at non-fundamental frequency and non-MMC characteristic subharmonic frequency, such as subsynchronous frequency range, in and among MMC-HVDC stations. When the voltage on the DC side fluctuates by delta VdcOne fluctuation frequency in the series circuit is superposed with the inherent resonance frequency of the equivalent resistor, capacitor and inductor series circuit at the DC side of the MMC-HVDCAnd then the voltage fluctuation can become an excitation source of MMC-HVDC side resonance to excite end-to-end MMC-HVDC side station resonance. The MMC-HVDC dc side resonant current will increase system losses and may cause MMC latch-up or even outage.
The modular multilevel converter and MMC-based flexible DC power transmission topology is shown in the attached figures 1 and 2, wherein in the attached figure 1, L1、L2Respectively an equivalent inductance L of an alternating current system 1 and an alternating current system 2s1、Ls2The outlet flat wave inductors of MMC1 and MMC2 are provided. Unlike the topology of a two-level converter adopting a direct-current side centralized capacitor, the MMC adopts a discrete capacitor structure, and as shown in the attached drawing and 2, the capacitor is respectively arranged in each submodule of a three-phase upper bridge arm and a three-phase lower bridge arm. At any moment, the sum of the numbers of the submodules thrown into the upper and lower bridge arms of each phase
Figure GDA0003119742940000011
VdcNTo a rated value of DC voltage, VsmNIs the sub-module voltage rating. Deducing the equivalent capacitance of each phase unit (each phase upper bridge arm and lower bridge arm are collectively called as a phase unit) of the MMC according to energy conservation
Figure GDA0003119742940000012
CsmIs the sub-module capacitance value.
The MMC control system comprises a main control part and a valve control part, wherein the main control part comprises an outer ring control module, an inner ring current control module, a circulating current inhibition module, a negative sequence current inhibition module and a bridge arm reference voltage generation module, and the valve control part comprises a nearest level approximation modulation algorithm and a capacitance voltage balance algorithm, as shown in figure 3.
The end-to-end MMC-HVDC DC side equivalent circuit and LC resonance circuit are shown in figure 3, wherein Req1、Req2Bridge arm loss equivalent resistances of MMC1 and MMC 2; l isarm1、Larm2Bridge arm inductors of MMC1 and MMC2 respectively; l iss1、Ls2The outgoing line flat wave inductors are respectively MMC1 and MMC 2; rline、LlineRespectively an equivalent resistance and an equivalent inductance of the circuit; cjpeq1、Cjneq1MMC1 upper bridge arm and lower bridge armEquivalent capacitance of bridge arm, Cjpeq2、Cjneq2(j ═ a, b, c) are equivalent capacitances of the upper arm and the lower arm of MMC2, respectively, and satisfy
Figure GDA0003119742940000021
Figure GDA0003119742940000022
Csm1、Csm2The sub-module capacitance values of MMC1 and MMC 2.
There are multiple RLC resonant loops on the MMC-HVDC dc side. When the main circuit parameters of the MMC are selected in engineering, the principle of avoiding resonance in the MMC station or between the MMC stations at fundamental frequency and MMC characteristic subharmonic frequency is adopted. Assuming that the number of the submodules input by the phase unit is N and the harmonic frequency is N, the main circuit parameters meet the requirements
Figure GDA0003119742940000023
i＝1,2，……，ω0Is the fundamental angular frequency. An equivalent circuit of the MMC-HVDC interstation resonance is shown in figure 5. The dotted loop with arrow in FIG. 5 represents the resonant loop between stations, Req、Leq、CeqThe MMC-HVDC circuit is characterized in that a virtual resistor is introduced into an equivalent resistor, an equivalent inductor and an equivalent capacitor on the front direct current side of the MMC-HVDC circuit respectively. Δ VdcFor MMC-HVDC side voltage fluctuation, have
Figure GDA0003119742940000024
In order to avoid the resonance between MMC stations, the main circuit parameters need to meet
Figure GDA0003119742940000025
Figure GDA0003119742940000026
For MMC-HVDC side, the medium angular frequency is niω0Of the voltage fluctuation of (1), niIs the ratio of the voltage fluctuation frequency of the direct current side to the fundamental frequency,
Figure GDA0003119742940000027
as a direct side angular frequencyIs niω0The phase of the voltage fluctuation.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method and a device for inhibiting end-to-end MMC-HVDC direct-current side station resonance.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
the invention provides a method for inhibiting resonance between end-to-end MMC-HVDC direct current side stations, which comprises the following steps:
extracting direct current fluctuation components from direct current, and determining the resistance value of a virtual resistor introduced from the MMC-HVDC direct current side;
determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor;
and determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor.
The extracting of the dc current fluctuation component from the dc current includes:
let the direct current be idcAccording to idcCalculating the direct current component of the direct current, comprising:
idc0＝average(idc) (1)
wherein idc0For the direct current component of the direct current, average () is the average window filter function;
setting the DC current fluctuation component as
Figure GDA0003119742940000031
It is expressed as:
Figure GDA0003119742940000032
the step of determining the resistance value of the virtual resistor introduced by the MMC direct current side comprises the following steps:
according to the end-to-end MMC-HVDC side equivalent circuit, the end-to-end MMC-HVDC side equivalent impedance Z can be obtainedeq(n) which is represented as:
Figure GDA0003119742940000033
wherein n is the harmonic order, ω0At fundamental angular frequency, Req1、Req2Bridge arm loss equivalent resistance, L, of MMC1 and MMC2 respectivelyarm1、Larm2Bridge arm inductances, L, of MMC1, MMC2, respectivelys1、Ls2Outlet flat wave inductance, R, of MMC1 and MMC2 respectivelyline、LlineRespectively equivalent resistance and inductance of the DC line, Csm1、Csm2Sub-module capacitance values, R, of MMC1 and MMC2 respectivelyeq、Leq、CeqRespectively an equivalent resistor, an equivalent inductor and an equivalent capacitor at the direct current side of the MMC-HVDC before introducing the virtual resistor, wherein N is the number of sub-modules input by an upper bridge arm and a lower bridge arm of each phase of the MMC;
obtained according to formula (3):
Figure GDA0003119742940000034
Figure GDA0003119742940000035
Figure GDA0003119742940000036
introducing a virtual resistor at the MMC-HVDC side, wherein the voltage fluctuation delta V of the MMC-HVDC side is realizeddcAnd MMC-HVDC side current fluctuation Delta IdcSatisfies the following conditions:
Figure GDA0003119742940000041
wherein s is Laplace operator, ξ is second-order oscillation circuit damping coefficient, REQFor introducing an equivalent resistance omega on the direct current side of MMC-HVDC after the virtual resistancenIs the natural resonant angular frequency of the second-order oscillation circuit and meets the requirement
Figure GDA0003119742940000042
Obtained according to equation (7):
Figure GDA0003119742940000043
the introduction of the virtual resistor on the DC side of the MMC-HVDC leads the equivalent resistance on the DC side of the MMC-HVDC to be increased, REQAnd ReqSatisfies the following conditions:
Figure GDA0003119742940000044
wherein R isvIs the resistance value of the virtual resistor;
obtained according to formula (4) and formula (9):
Figure GDA0003119742940000045
according to the formula (10), the following can be obtained:
Figure GDA0003119742940000046
the step of determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor comprises the following steps:
the voltage drop component of the virtual resistance is denoted by Δ v, and there are:
Figure GDA0003119742940000047
wherein R isvIs the resistance value of the virtual resistor,
Figure GDA0003119742940000048
is a dc current ripple component.
The step of determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor comprises the following steps:
after the virtual resistor is introduced, the reference voltage of the MMC bridge arm is expressed as follows:
Figure GDA0003119742940000051
wherein p represents an MMC upper bridge arm, n' represents an MMC lower bridge arm, and an intermediate quantity j is a, b, c, vpjFor introducing a j-phase reference voltage v of an upper bridge arm of the MMC after a virtual resistor is introducedn'jFor introducing a j-phase reference voltage V of a lower bridge arm of the MMC after a virtual resistor is introduceddcIs a direct voltage, v+jIs a j-phase positive sequence reference voltage, v-jIs a j-phase negative sequence reference voltage, vcirjΔ v is a voltage drop component of the virtual resistance for the circulating current suppression reference voltage.
The invention also provides a device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations, which comprises:
means for extracting a dc current ripple component from the dc current and determining a resistance value of a virtual resistor introduced at the MMC-HVDC dc side;
means for determining a voltage drop component of the virtual resistor based on the extracted direct current fluctuation component and a resistance value of the virtual resistor; and
and the device is used for determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor.
The device for extracting the direct current fluctuation component from the direct current and determining the resistance value of the virtual resistor introduced into the MMC-HVDC direct current side comprises the following steps:
means for extracting a dc current ripple component from the dc current; and
and the device is used for determining the resistance value of the virtual resistor introduced by the MMC-HVDC direct current side.
The apparatus for extracting a dc current ripple component from a dc current includes:
for according to idc0＝average(idc) Means for determining the DC component of the DC current idcIs a direct current idc0For the direct current component of the direct current, average () is the average window filter function;
for in accordance with
Figure GDA0003119742940000052
Determining a DC current ripple component
Figure GDA0003119742940000053
The apparatus of (1).
The means for determining the voltage drop component of the virtual resistor based on the extracted DC current fluctuation component and the resistance value of the virtual resistor
Figure GDA0003119742940000054
Determining a voltage drop component Deltav, R of a virtual resistancevIs the resistance value of the virtual resistor,
Figure GDA0003119742940000055
is a dc current ripple component.
The device for determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor
Figure GDA0003119742940000056
Determining the reference voltage of an MMC bridge arm after introducing the virtual resistor, wherein p represents an MMC upper bridge arm, n' represents an MMC lower bridge arm, and the intermediate quantity j is equal to a, b, c, vpjFor introducing a j-phase reference voltage v of an upper bridge arm of the MMC after a virtual resistor is introducedn'jFor introducing a j-phase reference voltage V of a lower bridge arm of the MMC after a virtual resistor is introduceddcIs a direct voltage, v+jIs a j-phase positive sequence reference voltage, v-jIs a j-phase negative sequence reference voltage, vcirjΔ v is the voltage drop of the virtual resistor for circulating current suppression reference voltageAmount of the compound (A).
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
1. the method for inhibiting the resonance between the end-to-end MMC-HVDC direct-current side stations can inhibit the generation of the MMC-HVDC direct-current side current resonance under the condition of not increasing extra loss and reduce the possibility of the generation of MMC-HVDC direct-current side faults, thereby improving the utilization efficiency of the voltage source converter and saving the cost;
2. according to the method for inhibiting the inter-station resonance of the end-to-end MMC-HVDC direct current side, the equivalent position of the virtual resistor is on the bridge arm, so that the in-station resonance is also inhibited;
3. the method for inhibiting the resonance between the end-to-end MMC-HVDC direct current side stations is mainly realized by improving the upper control of the MMC, and is easy to implement.
Drawings
FIG. 1 is a schematic diagram of an end-to-end MMC-HVDC topology;
FIG. 2 is a schematic diagram of an MMC topology;
FIG. 3 is a schematic diagram of an MMC control system architecture;
FIG. 4 is a schematic diagram of an end-to-end MMC-HVDC direct current side equivalent circuit and an LC resonant tank;
FIG. 5 is a schematic diagram of an end-to-end MMC-HVDC direct current side simplified equivalent circuit and an inter-station resonance equivalent circuit;
FIG. 6 is a schematic structural diagram of an MMC control system after a virtual resistor is introduced into a bridge arm;
FIG. 7 is a schematic diagram of the equivalent positions of the virtual resistors in the bridge arms;
FIG. 8 is a schematic diagram of an end-to-end MMC-HVDC direct-current side equivalent circuit after a bridge arm introduces a virtual resistor;
FIG. 9 is a schematic diagram of an end-to-end MMC-HVDC direct-current side simplified equivalent circuit and an inter-station resonance equivalent circuit after virtual resistors are introduced into bridge arms.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Although MMC-HVDC considers MMC-The resonance characteristic in and between HVDC stations avoids the possibility of resonance of MMC-HVDC at fundamental frequency and characteristic subharmonic frequency in the aspect of main circuit parameter selection, but the MMC-HVDC direct-current side equivalent circuit still has inherent resonance frequency, and the MMC-HVDC stations and the stations are possible to resonate at non-fundamental frequency and non-MMC characteristic subharmonic frequency, such as a subsynchronous frequency range. When the voltage of the MMC-HVDC side fluctuates by delta VdcWhen a certain fluctuation frequency in the voltage fluctuation circuit coincides with the inherent resonance frequency of the MMC-HVDC direct-current side equivalent circuit, the voltage fluctuation becomes an excitation source of MMC-HVDC direct-current side resonance.
As can be known from an end-to-end MMC-HVDC side equivalent circuit (see attached figure 5), the current resonance peak value of the MMC-HVDC side can be restrained by increasing the equivalent resistance of the DC side. The invention aims to increase the equivalent resistance of the direct current side of the bridge arm without increasing the system loss and reduce the amplitude of the resonant current of the MMC-HVDC direct current side by introducing the voltage drop component of the virtual resistance into the reference voltage of the bridge arm, thereby achieving the purpose of inhibiting the resonance between end-to-end MMC-HVDC direct current side stations.
The invention provides a method for inhibiting resonance between end-to-end MMC-HVDC direct current side stations, which comprises the following steps:
extracting direct current fluctuation components from direct current, and determining the resistance value of a virtual resistor introduced from the MMC-HVDC direct current side;
determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor;
and determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor.
In order to ensure the introduction of a dummy resistor RvWithout introducing DC bias into MMC DC voltage, virtual resistor RvOnly non-direct current can be acted, so that the direct current component of the direct current is extracted through average value filtering, and then the difference between the direct current component and the direct current is made to obtain the fluctuation component in the direct current side current. Extracting the dc current ripple component from the dc current includes:
let the direct current be idcAccording to idcCalculating the direct current component of the direct current, comprising:
idc0＝average(idc) (1)
wherein idc0The average () is a mean value window filter function, the typical value of the sampling frequency is 3200Hz, and other reasonable sampling frequencies can also be adopted;
setting the DC current fluctuation component as
Figure GDA0003119742940000071
It is expressed as:
Figure GDA0003119742940000072
to calculate the voltage drop component on the virtual resistor, the magnitude of the resistance value of the virtual resistor is calculated, the too small value of the resistance value of the virtual resistor cannot inhibit the peak value of the resonant current, and the too large value of the resistance value causes the fluctuation of the direct current voltage to exceed the allowable range, so that reasonable design and calculation are required. Determining the resistance value of the virtual resistor introduced by the MMC direct current side comprises the following steps:
according to an end-to-end MMC-HVDC direct current side equivalent circuit (shown in figure 4), an end-to-end MMC-HVDC direct current side equivalent impedance Z can be obtainedeq(n) which is represented as:
Figure GDA0003119742940000081
wherein n is the harmonic order, ω0At fundamental angular frequency, Req1、Req2Bridge arm loss equivalent resistance, L, of MMC1 and MMC2 respectivelyarm1、Larm2Bridge arm inductances, L, of MMC1, MMC2, respectivelys1、Ls2Outlet flat wave inductance, R, of MMC1 and MMC2 respectivelyline、LlineRespectively equivalent resistance and inductance of the DC line, Csm1、Csm2Sub-module capacitance values, R, of MMC1 and MMC2 respectivelyeq、Leq、CeqRespectively an equivalent resistance, an equivalent inductance and an equivalent capacitance at the DC side of the MMC-HVDC before introducing the virtual resistance, wherein N is the upper part and the lower part of each phase of the MMCThe number of submodules thrown by the bridge arm;
obtained according to formula (3):
Figure GDA0003119742940000082
Figure GDA0003119742940000083
Figure GDA0003119742940000084
after the virtual resistor is introduced, the end-to-end MMC-HVDC side simplified equivalent circuit is still an RLC series circuit (see attached figure 9), the virtual resistor is introduced into the MMC-HVDC side, and the voltage fluctuation delta V of the MMC-HVDC side is realized at the momentdcAnd MMC-HVDC side current fluctuation Delta IdcSatisfies the following conditions:
Figure GDA0003119742940000085
wherein s is a Laplace operator; xi is a damping coefficient of the second-order oscillation circuit, and when the damping coefficient is 0.707, resonance is well damped; rEQThe method comprises the steps of introducing a virtual resistor to an MMC-HVDC direct current side equivalent resistor; omeganIs the natural resonant angular frequency of the second-order oscillation circuit and meets the requirement
Figure GDA0003119742940000086
The corresponding equivalence of the denominator coefficients in equation (7) yields:
Figure GDA0003119742940000091
the introduction of the virtual resistor on the DC side of the MMC-HVDC leads the equivalent resistance on the DC side of the MMC-HVDC to be increased, REQAnd ReqSatisfies the following conditions:
Figure GDA0003119742940000092
wherein R isvIs the resistance value of the virtual resistor;
obtained according to formula (4) and formula (9):
Figure GDA0003119742940000093
according to the formula (10), the following can be obtained:
Figure GDA0003119742940000094
the step of determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor comprises the following steps:
the voltage drop component of the virtual resistance is denoted by Δ v, and there are:
Figure GDA0003119742940000095
wherein R isvIs the resistance value of the virtual resistor,
Figure GDA0003119742940000096
is a dc current ripple component.
As can be known from an end-to-end MMC-HVDC inter-station resonance equivalent circuit (shown in an attached figure 5), increasing the equivalent resistance of the DC side can inhibit the current resonance of the MMC-HVDC side. In order to increase the equivalent resistance on the direct current side, a voltage drop component Δ v of a virtual resistor is introduced into the MMC bridge arm reference voltage, so that an MMC control system with a resonance suppression effect is formed (see fig. 6).
Determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor comprises the following steps:
after the virtual resistor is introduced, the reference voltage of the MMC bridge arm is expressed as follows:
Figure GDA0003119742940000097
wherein p represents an MMC upper bridge arm, n' represents an MMC lower bridge arm, and an intermediate quantity j is a, b, c, vpjFor introducing a j-phase reference voltage v of an upper bridge arm of the MMC after a virtual resistor is introducedn'jFor introducing a j-phase reference voltage V of a lower bridge arm of the MMC after a virtual resistor is introduceddcIs a direct voltage, v+jIs a j-phase positive sequence reference voltage, v-jIs a j-phase negative sequence reference voltage, vcirjΔ v is a voltage drop component of the virtual resistance for the circulating current suppression reference voltage.
The introduction of the voltage drop component of the virtual resistor into the bridge arm reference voltage generation module of the MMC control system is equivalent to the addition of R on the bridge arm by using a control meansvThe virtual resistance of (see fig. 7). For an opposite-end MMC-HVDC, the size of each bridge arm equivalent to two MMC valves is increased by RvThe virtual resistance of (see fig. 8). On the whole, after voltage drop components of the virtual resistors are introduced into MMC bridge arm voltage reference values, the equivalent resistance of the direct current side of the end-to-end MMC-HVDC is increased by 4RvAnd/3 (see figure 9), the amplitude of the resonant current of the MMC-HVDC direct-current side is reduced, and therefore the aim of inhibiting the resonance between the end-to-end MMC-HVDC direct-current side stations is achieved.
The invention also provides a device for inhibiting resonance between end-to-end MMC-HVDC direct current side stations, which comprises:
means for extracting a dc current ripple component from the dc current and determining a resistance value of a virtual resistor introduced at the MMC-HVDC dc side;
means for determining a voltage drop component of the virtual resistor based on the extracted direct current fluctuation component and a resistance value of the virtual resistor; and
and the device is used for determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor.
The device for extracting the direct current fluctuation component from the direct current and determining the resistance value of the virtual resistor introduced into the MMC-HVDC direct current side comprises the following steps:
means for extracting a dc current ripple component from the dc current; and
and the device is used for determining the resistance value of the virtual resistor introduced by the MMC-HVDC direct current side.
The apparatus for extracting a dc current ripple component from a dc current includes:
for according to idc0＝average(idc) Means for determining the DC component of the DC current idcIs a direct current idc0For the direct current component of the direct current, average () is the average window filter function;
for in accordance with
Figure GDA0003119742940000101
Determining a DC current ripple component
Figure GDA0003119742940000102
The apparatus of (1).
The means for determining the voltage drop component of the virtual resistor based on the extracted DC current fluctuation component and the resistance value of the virtual resistor
Figure GDA0003119742940000103
Determining a voltage drop component Deltav, R of a virtual resistancevIs the resistance value of the virtual resistor,
Figure GDA0003119742940000104
is a dc current ripple component.
The device for determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor
Figure GDA0003119742940000105
Determining the reference voltage of an MMC bridge arm after introducing the virtual resistor, wherein p represents an MMC upper bridge arm, n' represents an MMC lower bridge arm, and the intermediate quantity j is equal to a, b, c, vpjFor introducing a j-phase reference voltage v of an upper bridge arm of the MMC after a virtual resistor is introducedn'jFor introducing a j-phase reference voltage V of a lower bridge arm of the MMC after a virtual resistor is introduceddcIs a direct voltage, v+jIs a j-phase positive sequence reference voltage, v-jIs j phase negativeSequence reference voltage, vcirjΔ v is a voltage drop component of the virtual resistance for the circulating current suppression reference voltage.
Finally, it should be noted that: the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person of ordinary skill in the art can make modifications or equivalents to the specific embodiments of the present invention with reference to the above embodiments, and such modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims of the present invention as set forth in the claims.

Claims (2)

1. A method of suppressing resonance between end-to-end MMC-HVDC direct current side stations, the method comprising:
extracting direct current fluctuation components from direct current, and determining the resistance value of a virtual resistor introduced from the MMC-HVDC direct current side;
determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor;
determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor;
the extracting of the dc current fluctuation component from the dc current includes:
let the direct current be idcAccording to idcCalculating the direct current component of the direct current, comprising:
idc0＝average(idc) (1)
wherein idc0For the direct current component of the direct current, average () is the average window filter function;
setting the DC current fluctuation component as
Figure FDA0003119742930000011
It is expressed as:
Figure FDA0003119742930000012
the step of determining the resistance value of the virtual resistor introduced by the MMC direct current side comprises the following steps:
according to the end-to-end MMC-HVDC side equivalent circuit, the end-to-end MMC-HVDC side equivalent impedance Z can be obtainedeq(n) which is represented as:
Figure FDA0003119742930000013
wherein n is the harmonic order, ω0At fundamental angular frequency, Req1、Req2Bridge arm loss equivalent resistance, L, of MMC1 and MMC2 respectivelyarm1、Larm2Bridge arm inductances, L, of MMC1, MMC2, respectivelys1、Ls2Outlet flat wave inductance, R, of MMC1 and MMC2 respectivelyline、LlineRespectively equivalent resistance and inductance of the DC line, Csm1、Csm2Sub-module capacitance values, R, of MMC1 and MMC2 respectivelyeq、Leq、CeqRespectively an equivalent resistor, an equivalent inductor and an equivalent capacitor at the direct current side of the MMC-HVDC before introducing the virtual resistor, wherein N is the number of sub-modules input by an upper bridge arm and a lower bridge arm of each phase of the MMC;
obtained according to formula (3):
Figure FDA0003119742930000014
Figure FDA0003119742930000021
Figure FDA0003119742930000022
introducing a virtual resistor at the MMC-HVDC side, wherein the voltage fluctuation delta V of the MMC-HVDC side is realizeddcAnd MMC-HVDC side current fluctuation Delta IdcSatisfies the following conditions:
Figure FDA0003119742930000023
wherein s is Laplace operator, ξ is second-order oscillation circuit damping coefficient, REQFor introducing an equivalent resistance omega on the direct current side of MMC-HVDC after the virtual resistancenIs the natural resonant angular frequency of the second-order oscillation circuit and meets the requirement
Figure FDA0003119742930000024
Obtained according to equation (7):
Figure FDA0003119742930000025
the introduction of the virtual resistor on the DC side of the MMC-HVDC leads the equivalent resistance on the DC side of the MMC-HVDC to be increased, REQAnd ReqSatisfies the following conditions:
Figure FDA0003119742930000026
wherein R isvIs the resistance value of the virtual resistor;
obtained according to formula (4) and formula (9):
Figure FDA0003119742930000027
according to the formula (10), the following can be obtained:
Figure FDA0003119742930000028
the step of determining the voltage drop component of the virtual resistor according to the extracted direct current fluctuation component and the resistance value of the virtual resistor comprises the following steps:
the voltage drop component of the virtual resistance is denoted by Δ v, and there are:
Figure FDA0003119742930000031
wherein R isvIs the resistance value of the virtual resistor,
Figure FDA0003119742930000032
is a direct current fluctuation component;
the step of determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor comprises the following steps:
after the virtual resistor is introduced, the reference voltage of the MMC bridge arm is expressed as follows:
Figure FDA0003119742930000033
wherein p represents an MMC upper bridge arm, n' represents an MMC lower bridge arm, and an intermediate quantity j is a, b, c, vpjFor introducing a j-phase reference voltage v of an upper bridge arm of the MMC after a virtual resistor is introducedn'jFor introducing a j-phase reference voltage V of a lower bridge arm of the MMC after a virtual resistor is introduceddcIs a direct voltage, v+jIs a j-phase positive sequence reference voltage, v-jIs a j-phase negative sequence reference voltage, vcirjΔ v is a voltage drop component of the virtual resistance for the circulating current suppression reference voltage.
2. An apparatus for suppressing resonance between end-to-end MMC-HVDC direct current side stations, characterized in that the apparatus is adapted to perform the method of claim 1;
the device comprises:
means for extracting a dc current ripple component from the dc current and determining a resistance value of a virtual resistor introduced at the MMC-HVDC dc side;
means for determining a voltage drop component of the virtual resistor based on the extracted direct current fluctuation component and a resistance value of the virtual resistor; and
the device is used for determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor;
the device for extracting the direct current fluctuation component from the direct current and determining the resistance value of the virtual resistor introduced into the MMC-HVDC direct current side comprises the following steps:
means for extracting a dc current ripple component from the dc current; and
means for determining the resistance of the virtual resistor introduced by the MMC-HVDC direct current side;
the apparatus for extracting a dc current ripple component from a dc current includes:
for according to idc0＝average(idc) Means for determining the DC component of the DC current idcIs a direct current idc0For the direct current component of the direct current, average () is the average window filter function;
for in accordance with
Figure FDA0003119742930000034
Determining a DC current ripple component
Figure FDA0003119742930000035
The apparatus of (1);
the means for determining the voltage drop component of the virtual resistor based on the extracted DC current fluctuation component and the resistance value of the virtual resistor
Figure FDA0003119742930000041
Determining a voltage drop component Deltav, R of a virtual resistancevIs the resistance value of the virtual resistor,
Figure FDA0003119742930000042
is a direct current fluctuation component;
the device for determining the MMC bridge arm reference voltage after the virtual resistor is introduced according to the voltage drop component of the virtual resistor
Figure FDA0003119742930000043
Determining MMC bridge arm reference after introducing virtual resistanceVoltage, p denotes the MMC upper arm, n' denotes the MMC lower arm, intermediate quantity j ═ a, b, c, vpjFor introducing a j-phase reference voltage v of an upper bridge arm of the MMC after a virtual resistor is introducedn'jFor introducing a j-phase reference voltage V of a lower bridge arm of the MMC after a virtual resistor is introduceddcIs a direct voltage, v+jIs a j-phase positive sequence reference voltage, v-jIs a j-phase negative sequence reference voltage, vcirjΔ v is a voltage drop component of the virtual resistance for the circulating current suppression reference voltage.
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