CN111446843B - Transient current calculation method for circulation current of modular multilevel voltage source converter valve - Google Patents

Transient current calculation method for circulation current of modular multilevel voltage source converter valve Download PDF

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CN111446843B
CN111446843B CN202010363488.XA CN202010363488A CN111446843B CN 111446843 B CN111446843 B CN 111446843B CN 202010363488 A CN202010363488 A CN 202010363488A CN 111446843 B CN111446843 B CN 111446843B
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bridge arm
current
modular multilevel
inductor
inductance
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CN111446843A (en
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胡应宏
龙凯华
彭珑
赵媛
张静岚
蔡巍
刘羿辰
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State Grid Corp of China SGCC
North China Electric Power Research Institute Co Ltd
Electric Power Research Institute of State Grid Jibei Electric Power Co Ltd
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State Grid Corp of China SGCC
North China Electric Power Research Institute Co Ltd
Electric Power Research Institute of State Grid Jibei 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
    • 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
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • 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
    • 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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0009—Devices or circuits for detecting current in a converter
    • 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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
    • 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 transient current calculation method for a modular multilevel voltage source converter valve circulating current, which comprises the following steps: the method comprises the steps of collecting bridge arm currents and output currents of a modular multilevel converter, wherein the bridge arm currents comprise an upper bridge arm current and a lower bridge arm current; determining a double-frequency component and a quadruple-frequency component of the circulating transient current according to inductance parameters of the coupling inductance, bridge arm current, output current, a second harmonic component formula and a fourth harmonic component formula, and further obtaining bridge arm circulating current; and determining the reference voltage of the modular multilevel converter according to the bridge arm circulation current so as to inhibit the bridge arm circulation current.

Description

Transient current calculation method for circulation current of modular multilevel voltage source converter valve
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to a transient current calculation method for circulating current of a modular multilevel voltage source converter valve.
Background
The Modular Multilevel Converter (Modular Multilevel Converter MMC) adopts a controllable turn-off power electronic device and a Pulse Width Modulation (PWM) technology, can realize independent control of active power and reactive power, can supply power to a passive network, is a novel Multilevel Converter, and has become a research hotspot in the current international power electronic field.
In the middle of the MMC system, there is interior circulation, and too big bridge arm circulation can influence MMC's system performance, influences MMC's steady operation even when serious. Because the coupling inductor has the advantages of small volume, fast transient response, high rated saturation current and the like, the coupling inductor is introduced into the research of many power electronic fields at present, and the research proves that the volume and the weight of the coupling inductor can be reduced by 40 percent under the condition of the same circulating current inhibition effect. However, at present, transient state circulating current of a modular multilevel converter adopting coupling inductance cannot be accurately calculated, the influence of the transient state circulating current cannot be accurately determined, and the circulating current suppression effect can be influenced.
Disclosure of Invention
The invention aims to provide a transient current calculation method for the circulating current of a modular multilevel voltage source converter valve, which takes quadruple frequency current into consideration and obviously improves the accuracy of circulating current calculation. Another object of the present invention is to provide a transient current calculation system for circulating current of a modular multilevel voltage source converter valve. The invention also discloses computer equipment. The invention also discloses a readable medium.
In order to achieve the above object, the present invention discloses a transient current calculation method for a circulating current of a modular multilevel voltage source converter valve, including:
the method comprises the steps of collecting bridge arm currents and output currents of a modular multilevel converter, wherein the bridge arm currents comprise an upper bridge arm current and a lower bridge arm current;
determining a double-frequency component and a quadruple-frequency component of the circulating transient current according to inductance parameters of the coupling inductance, bridge arm current, output current, a second harmonic component formula and a fourth harmonic component formula, and further obtaining bridge arm circulating current;
and determining the reference voltage of the modular multilevel converter according to the bridge arm circulation current so as to inhibit the bridge arm circulation current.
Preferably, the method further comprises, before collecting the bridge arm current and the output current of the modular multilevel converter:
the coupling inductor is equivalent to a discrete inductor;
determining output voltages of an upper bridge arm and a lower bridge arm of an equivalent discrete inductance modular multilevel converter so as to obtain the output voltages of the bridge arms;
and performing Fourier expansion on the output voltage of the bridge arm to obtain a second harmonic component formula and a fourth harmonic component formula.
Preferably, the step of equating the coupling inductor to a discrete inductor specifically includes:
determining the voltage drop of the coupling inductor according to the first sub-inductor, the second sub-inductor, the bridge arm current and the output current of the coupling inductor;
and the coupling inductor is equivalent to a discrete inductor according to the voltage drop of the coupling inductor.
Preferably, the determining the output voltages of the upper bridge arm and the lower bridge arm of the equivalent discrete inductance modular multilevel converter to obtain the output voltage of the bridge arm specifically includes:
determining the upper bridge arm current and the lower bridge arm current of the coupling inductor with the quadruple frequency components considered;
determining switching functions of an upper bridge arm and a lower bridge arm according to a preset switching function and performing Fourier expansion to obtain average currents of any capacitors of the upper bridge arm and the lower bridge arm of the modular multilevel converter;
performing Fourier expansion on the average current, and combining a capacitive reactance to obtain sub-module voltages of an upper bridge arm and a lower bridge arm;
and obtaining output voltages of the upper bridge arm and the lower bridge arm according to the sub-module voltage and the switching function, and further obtaining the output voltages of the bridge arms.
Preferably, the second harmonic component formula and the fourth harmonic component formula are respectively:
Figure GDA0003019632050000031
wherein A and B are parameters,
Figure GDA0003019632050000032
representing the phase angle of the fundamental wave, N is the number of submodules in each bridge arm, omega is the angular frequency of the fundamental wave output by the converter, C is the capacitance value of the submodule of the bridge arm, and Leq＝L1+L2M, M represents the mutual inductance between the coupled inductors, L1Inductance value of the first sub-inductor of the coupling inductor, L2The inductance of the second sub-inductor for the coupling inductor, m represents the modulation ratio, IaExpressed as the effective value of the fundamental wave of the output current on the AC side, IadIs the dc component in the bridge arm current.
The invention also discloses a transient current calculation system for the circulation current of the modular multilevel voltage source converter valve, which comprises the following steps:
the current acquisition module is used for acquiring bridge arm currents and output currents of the modular multilevel converter, wherein the bridge arm currents comprise an upper bridge arm current and a lower bridge arm current;
the loop current determining module is used for determining a frequency doubling component and a frequency quadrupling component of the loop current transient state current according to the inductance parameter of the coupling inductance, the bridge arm current, the output current, a second harmonic component formula and a fourth harmonic component formula and further obtaining the bridge arm loop current;
and the circulating current suppression module is used for determining the reference voltage of the modular multilevel converter according to the bridge arm circulating current so as to suppress the bridge arm circulating current.
Preferably, the model establishing module is further used for equating the coupling inductance to a discrete inductance, determining output voltages of an upper bridge arm and a lower bridge arm of the equivalent discrete inductance modular multilevel converter, further obtaining the output voltages of the bridge arms, and performing fourier expansion on the output voltages of the bridge arms to obtain a second harmonic component formula and a fourth harmonic component formula.
Preferably, the model establishing module is specifically configured to determine a voltage drop of the coupling inductor according to the first sub-inductor, the second sub-inductor, the bridge arm current, and the output current of the coupling inductor; and the coupling inductor is equivalent to a discrete inductor according to the voltage drop of the coupling inductor.
Preferably, the model establishing module is specifically configured to determine the upper bridge arm current and the lower bridge arm current of the coupling inductor, which take the quadruple frequency component into consideration; determining switching functions of an upper bridge arm and a lower bridge arm according to a preset switching function and performing Fourier expansion to obtain average currents of any capacitors of the upper bridge arm and the lower bridge arm of the modular multilevel converter; performing Fourier expansion on the average current, and combining a capacitive reactance to obtain sub-module voltages of an upper bridge arm and a lower bridge arm; and obtaining output voltages of the upper bridge arm and the lower bridge arm according to the sub-module voltage and the switching function, and further obtaining the output voltages of the bridge arms.
Preferably, the second harmonic component formula and the fourth harmonic component formula are respectively:
Figure GDA0003019632050000041
wherein A and B are parameters,
Figure GDA0003019632050000042
representing the phase angle of the fundamental wave, N is the number of submodules in each bridge arm, omega is the angular frequency of the fundamental wave output by the converter, C is the capacitance value of the submodule of the bridge arm, and Leq＝L1+L2M, M represents the mutual inductance between the coupled inductors, L1Inductance value of the first sub-inductor of the coupling inductor, L2The inductance of the second sub-inductor for the coupling inductor, m represents the modulation ratio, IaExpressed as the effective value of the fundamental wave of the output current on the AC side, IadIs the dc component in the bridge arm current.
The invention also discloses a computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor,
the processor, when executing the program, implements the method as described above.
The invention also discloses a computer-readable medium, having stored thereon a computer program,
which when executed by a processor implements the method as described above.
According to the invention, a second harmonic component formula and a fourth harmonic component formula are used for calculating to obtain a second frequency component and a fourth frequency component of the circulating current transient state current of the coupling inductance modular multilevel converter, and further the bridge arm circulating current is obtained. According to the method, the influence of quadruple frequency current is considered when the transient current of the converter valve circulating current is calculated, and the accuracy of circulating current estimation is obviously improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart illustrating one embodiment of a method for calculating a transient current of a circulating current of a modular multilevel voltage source converter valve according to the present invention;
FIG. 2 is a second flowchart illustrating a method for calculating a transient current of a circulating current of a modular multilevel voltage source converter valve according to an embodiment of the present invention;
FIG. 3 is a third flowchart illustrating a method for calculating a transient current of a circulating current of a modular multilevel voltage source converter valve according to an embodiment of the invention;
fig. 4 is a circuit diagram of a coupling inductor connected to a dotted terminal in an embodiment of a method for calculating a transient current of a circulating current of a modular multilevel voltage source converter valve according to the invention;
fig. 5 is a circuit diagram of a coupling inductor connected to a different name terminal in an embodiment of a transient current calculation method for a modular multilevel voltage source converter valve loop current according to the invention;
fig. 6 is a circuit diagram of a discrete inductor equivalent to a coupling inductor connected to a dotted terminal in an embodiment of a transient current calculation method for a modular multilevel voltage source converter valve loop current according to the present invention;
fig. 7 is a circuit diagram of a discrete inductor equivalent to a coupling inductor connected to a different-name terminal according to an embodiment of a transient current calculation method for a modular multilevel voltage source converter valve loop current of the present invention;
FIG. 8 is a fourth flowchart illustrating a method for calculating a transient current of a circulating current of a modular multilevel voltage source converter valve according to an embodiment of the present invention;
FIG. 9 is a block diagram illustrating one embodiment of a transient current calculation system for circulating current of a modular multilevel voltage source converter valve according to the present invention;
FIG. 10 is a second block diagram of a transient current calculation system for circulating current of a modular multilevel voltage source converter valve according to an embodiment of the present invention;
FIG. 11 illustrates a schematic block diagram of a computer device suitable for use in implementing embodiments of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
According to one aspect of the invention, the embodiment discloses a transient current calculation method for circulating current of a modular multilevel voltage source converter valve. As shown in fig. 1, in this embodiment, the method includes:
s100: the method comprises the steps of collecting bridge arm currents and output currents of a modular multilevel converter, wherein the bridge arm currents comprise an upper bridge arm current and a lower bridge arm current.
S200: and determining a double-frequency component and a quadruple-frequency component of the circulating current transient state according to the inductance parameter of the coupling inductance, the bridge arm current, the output current, a second harmonic component formula and a fourth harmonic component formula, and further obtaining the bridge arm circulating current.
S300: and determining the reference voltage of the modular multilevel converter according to the bridge arm circulation current so as to inhibit the bridge arm circulation current.
According to the invention, a second harmonic component formula and a fourth harmonic component formula are used for calculating to obtain a second frequency component and a fourth frequency component of the circulating current transient state current of the coupling inductance modular multilevel converter, and further the bridge arm circulating current is obtained. According to the method, the influence of quadruple frequency current is considered when the transient current of the converter valve circulating current is calculated, and the accuracy of circulating current estimation is obviously improved.
In a preferred embodiment, as shown in fig. 2, the method further comprises, before collecting the bridge arm currents and the output currents of the modular multilevel converter:
s010: the coupled inductor is equivalent to a discrete inductor.
S020: and determining the output voltages of an upper bridge arm and a lower bridge arm of the equivalent discrete inductance modular multilevel converter so as to obtain the output voltages of the bridge arms.
S030: and performing Fourier expansion on the output voltage of the bridge arm to obtain a second harmonic component formula and a fourth harmonic component formula.
In a preferred embodiment, as shown in fig. 3, the S010 specifically includes:
s011: and determining the voltage drop of the coupling inductor according to the first sub-inductor, the second sub-inductor, the bridge arm current and the output current of the coupling inductor.
S012: and the coupling inductor is equivalent to a discrete inductor according to the voltage drop of the coupling inductor.
In an electrical circuit, when two coils are close enough, a change in the magnetic field caused by a change in current in one coil will affect the other coil, so-called magnetic coupling of the two coils, and so-called coupled inductance of the two coils as a whole. The unique property of the coupling inductor determines that the loop current is influenced after the bridge arm discrete inductor is replaced by the coupling inductor. The coupling inductance is connected in the same-name end and the different-name end, and the circuit structure is shown in fig. 4 and 5.
Firstly, analyzing the voltage of the coupling inductor, and when the homonymy end is connected to form the coupling inductor, obtaining the induced voltage drop on the inductor according to the magnetic flux relationship between each sub-inductor of the coupling inductor and the electromagnetic induction law, in a specific example, taking the homonymy end connection mode as an example, determining the induced voltage drop on each sub-inductor of the coupling inductor by the following formula:
Figure GDA0003019632050000071
wherein iUa/iUa(t) represents the upper arm current, iLa/iLa(t) represents the lower arm current, ia/ia(t) represents the a-phase output current, and the upper arm voltage of the coupled inductor is represented as uUa/uUa(t) lower arm voltage is denoted uLa/uLa(t), M represents mutual inductance between coupled inductors, L1Inductance value of the first sub-inductor of the coupling inductor, L2The inductance value of the second sub-inductor of the coupling inductor.
By performing an equivalent transformation on the formula (1), the following can be obtained:
Figure GDA0003019632050000072
according to the equivalent formula of the inductance-voltage drop of the formula (2), the equivalent circuit of the same-name end connection of the coupling inductor shown in the following fig. 6 can be obtained. Fig. 6 shows the relationship between the inductor voltages when the dotted terminals of the coupling inductor are connected, and the coupling inductor can be decoupled into a discrete inductor according to the relationship. After decoupling, for the connection of the terminals with the same name, the inductance of the bridge arm is reduced, and meanwhile, a derivative inductance is contributed to the load side, and the inductance is equal to the mutual inductance M.
Based on the same principle, the coupling inductors connected with the different name ends can be equivalent to an equivalent circuit shown in fig. 7 by using the same decoupling method based on the voltage equivalent relationship, and the inductance voltage drop expression of the upper bridge arm and the lower bridge arm is shown in the formula (3). And the equivalent inductance of the bridge arm is increased when the different-name end is adopted for connection, as opposed to the connection of the same-name end.
Figure GDA0003019632050000073
In a preferred embodiment, as shown in fig. 8, the S020 specifically includes:
s021: and determining the upper bridge arm current and the lower bridge arm current of the coupling inductor with the quadruple frequency components considered.
S022: and determining the switching functions of the upper bridge arm and the lower bridge arm according to the preset switching functions and performing Fourier expansion to obtain the average current of any capacitor of the upper bridge arm and the lower bridge arm of the modular multilevel converter.
S023: and performing Fourier expansion on the average current, and combining a capacitive reactance to obtain the sub-module voltages of the upper bridge arm and the lower bridge arm.
S024: and obtaining output voltages of the upper bridge arm and the lower bridge arm according to the sub-module voltage and the switching function, and further obtaining the output voltages of the bridge arms.
In order to accurately calculate the bridge arm circulation of the MMC, the influence of the quadruple frequency component on the circulation is introduced in the analysis process. The expression of the upper and lower bridge arm currents after the quadruple frequency component is considered is as follows:
Figure GDA0003019632050000081
wherein, IaExpressed as the effective value of the fundamental wave of the ac side output current,
Figure GDA0003019632050000086
representing the phase angle of the fundamental wave. I isadRepresenting the direct current component of the a-phase bridge arm current in the normal operation of the MMCIn the line case I can also be useddA/3 is represented bydIs the output current of the dc power supply. I is2Representing the magnitude of a double frequency component in the circulating current, theta representing its phase angle, I4Indicating the amplitude of the fourth harmonic, ξ indicating the phase angle of the fourth harmonic, t time, ω the converter output fundamental angular frequency.
In order to more clearly describe the action process of the submodule, a switching function S is introduced, and Q in the submodule is defined1Turn on Q2When the power is turned off, S is 1; q1Turn off Q2When turned on, S is 0. In the operation process of the MMC, all the sub-modules are regarded as a whole. With phase a as a reference, the switching equation of the upper and lower arms can be expressed as:
Figure GDA0003019632050000082
wherein S isUa_kRepresenting the switching function of the kth submodule of the upper bridge arm, SLa_kRepresents the switching function of the kth submodule of the lower bridge arm, SaAnd (4) representing the switching functions at two ends of the phase a, wherein N is the number of the submodules in each bridge arm.
The following equation can be expressed from equation (5) according to the fourier expansion:
Figure GDA0003019632050000083
wherein m represents a modulation ratio, AnIs the coefficient obtained by Fourier decomposition of the nth component, thetanIs the phase of the nth component obtained by fourier decomposition. When the number N of sub-modules is sufficiently large or the switching frequency is sufficiently high, the harmonic component in equation (6) is very small and negligible, so that in the case of high-frequency, multi-module, the average switching equation of a single sub-module can be expressed as equation (7), where
Figure GDA0003019632050000084
And
Figure GDA0003019632050000085
and respectively representing average switching functions of the upper bridge arm submodule and the lower bridge arm submodule.
Figure GDA0003019632050000091
When the MMC is in normal operation, the current i flowing through any sub-module can be obtainedsmk(t) is:
ismk(t)＝Sk(t)iU/L,x(t) (8)
wherein iU/L,x(t) represents a current flowing through the x-th phase upper arm or lower arm of the arm, Sk(t) is the Fourier-expanded switching function of the kth submodule, S is replaced by the mean switching equation of equation (7)k(t), the average current flowing through the sub-module capacitor can be represented by formula (9), where IPAnd INRespectively representing the average current flowing through the capacitors of the upper and lower bridge arm submodules.
Figure GDA0003019632050000092
By developing the above equation, equation (10) can be obtained, and the magnitude of each secondary component in the bridge arm current is given in detail by the following equation.
Figure GDA0003019632050000093
The nth component of the sub-module voltage may be obtained by multiplying the nth current harmonic by the capacitive reactance. Therefore, the fundamental frequency Δ u of the sub-module voltage can be obtained by multiplying the above formula by 1/(j ω C), 1/(j2 ω C), 1/(j3 ω C), 1/(j4 ω C), 1/(j5 ω C), wherein C is the capacitance value of the sub-module capacitor, j is the imaginary unit, and ω is the angular frequency of the output fundamental wave of the converterUc1(t) and. DELTA.uLc1(t), secondary frequency Δ uUc2(t) and. DELTA.uLc2(t), third order frequency Δ uUc3(t) and. DELTA.uLc3(t), quartic frequency Δ uUc4(t) and. DELTA.uLc4(t) frequency component Δ u of five timesUc5(t) and. DELTA.uLc5(t), the expressions of the components are respectively shown as the following formula:
Figure GDA0003019632050000094
Figure GDA0003019632050000101
Figure GDA0003019632050000102
Figure GDA0003019632050000103
Figure GDA0003019632050000104
the output voltage equation of the upper and lower bridge arms can be obtained by using the average switching equation and the submodule voltage equation as follows:
Figure GDA0003019632050000105
thus, the sum of the upper and lower arm voltages can be expressed as:
Δu(t)＝NΔuUo(t)+NΔuLo(t)＝Δu1(t)+Δu2(t)+Δu3(t)+Δu4(t)+Δu5(t) (17)
wherein, Δ u1(t)、Δu2(t)、Δu3(t)、Δu4(t) and. DELTA.u5(t) is the 1 st, 2 nd, 3 rd, 4 th and 5 th component of the bridge arm voltage.
And S030 performing Fourier expansion on the output voltage of the bridge arm to obtain a second harmonic component formula and a fourth harmonic component formula. Will show the formula (17)And on, obtaining a detailed expression of the sum of the upper and lower bridge arm voltages:
Figure GDA0003019632050000106
in the above formula, the ratio of the frequency doubling component to the frequency quadrupling component is the largest, so in the following analysis, only the influence of the frequency doubling component and the frequency quadrupling component on the circulating current is considered neglecting other high-order components, and the frequency doubling delta u is easy to obtain2(t) the expression is:
Figure GDA0003019632050000107
it is to be noted here that there are two unknowns in the calculation of the above-described second harmonic, i.e., the second harmonic component and the fourth harmonic component of the bridge arm loop current. Since the quadruplicate frequency component is relatively much smaller than the double frequency component, to solve the double frequency value, the last term in equation (19) is omitted, resulting in an approximate double frequency Δ u2e(t) is represented by the formula (20).
Figure GDA0003019632050000111
The fourth harmonic Deltau can be obtained by the same method4(t) the calculation formula is shown in formula (21).
Figure GDA0003019632050000112
Therefore, the second harmonic component and the fourth harmonic component in the MMC bridge arm loop can be expressed as follows:
Figure GDA0003019632050000113
in the formula, Leq is the equivalent inductance value of the bridge arm inductance, and the value is L which is different according to different inductance forms and connection modeseq＝L1+L2M. According to the method, the rear bridge arm with the coupling inductance taken into consideration can be clearly obtainedThe expressions of frequency doubling and frequency quadrupling in the circulating current can remarkably improve the accuracy of circulating current calculation after the frequency quadrupling current is taken into consideration.
Based on the same principle, the embodiment also discloses a transient current calculation system for the circulating current of the modular multilevel voltage source converter valve. As shown in fig. 9, in the present embodiment, the system includes a current collection module 11, a circulation current determination module 12, and a circulation current suppression module 13.
The current collection module 11 is configured to collect bridge arm currents and output currents of the modular multilevel converter, where the bridge arm currents include an upper bridge arm current and a lower bridge arm current.
The circulating current determining module 12 is configured to determine a double frequency component and a quadruple frequency component of the circulating transient current according to an inductance parameter of the coupling inductance, the bridge arm current, the output current, a second harmonic component formula and a fourth harmonic component formula, and further obtain the bridge arm circulating current.
And the circulating current suppression module 13 is used for determining a reference voltage of the modular multilevel converter according to the bridge arm circulating current so as to suppress the bridge arm circulating current.
In a preferred embodiment, as shown in FIG. 10, the system further comprises a model building module 10. The model establishing module 10 is configured to equate the coupling inductance to a discrete inductance, determine output voltages of an upper bridge arm and a lower bridge arm of the equivalent discrete inductance modular multilevel converter, further obtain the output voltages of the bridge arms, and perform fourier expansion on the output voltages of the bridge arms to obtain a second harmonic component formula and a fourth harmonic component formula.
In a preferred embodiment, the model building module 10 is specifically configured to determine a voltage drop of the coupling inductor according to the first sub-inductor, the second sub-inductor, the bridge arm current, and the output current of the coupling inductor; and the coupling inductor is equivalent to a discrete inductor according to the voltage drop of the coupling inductor.
In a preferred embodiment, the model building module 10 is specifically configured to determine the upper bridge arm current and the lower bridge arm current of the coupling inductor, which take the quadruple frequency component into consideration; determining switching functions of an upper bridge arm and a lower bridge arm according to a preset switching function and performing Fourier expansion to obtain average currents of any capacitors of the upper bridge arm and the lower bridge arm of the modular multilevel converter; performing Fourier expansion on the average current, and combining a capacitive reactance to obtain sub-module voltages of an upper bridge arm and a lower bridge arm; and obtaining output voltages of the upper bridge arm and the lower bridge arm according to the sub-module voltage and the switching function, and further obtaining the output voltages of the bridge arms.
Since the principle of the system for solving the problem is similar to the above method, the implementation of the system can refer to the implementation of the method, and the detailed description is omitted here.
The systems, devices, modules or units illustrated in the above embodiments may be implemented by a computer chip or an entity, or by a product with certain functions. A typical implementation device is a computer device, which may be, for example, a personal computer, a laptop computer, a cellular telephone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.
In a typical example, the computer device comprises in particular a memory, a processor and a computer program stored on the memory and executable on the processor, which when executed by the processor implements the method as described above.
Referring now to FIG. 11, shown is a schematic diagram of a computer device 600 suitable for use in implementing embodiments of the present application.
As shown in fig. 11, the computer apparatus 600 includes a Central Processing Unit (CPU)601 which can perform various appropriate works and processes according to a program stored in a Read Only Memory (ROM)602 or a program loaded from a storage section 608 into a Random Access Memory (RAM)) 603. In the RAM603, various programs and data necessary for the operation of the system 600 are also stored. The CPU601, ROM602, and RAM603 are connected to each other via a bus 604. An input/output (I/O) interface 605 is also connected to bus 604.
The following components are connected to the I/O interface 605: an input portion 606 including a keyboard, a mouse, and the like; an output section 607 including a Cathode Ray Tube (CRT), a liquid crystal feedback (LCD), and the like, and a speaker and the like; a storage section 608 including a hard disk and the like; and a communication section 609 including a network interface card such as a LAN card, a modem, or the like. The communication section 609 performs communication processing via a network such as the internet. The driver 610 is also connected to the I/O interface 605 as needed. A removable medium 611 such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, or the like is mounted on the drive 610 as necessary, so that a computer program read out therefrom is mounted as necessary on the storage section 608.
In particular, according to an embodiment of the present invention, the processes described above with reference to the flowcharts may be implemented as computer software programs. For example, embodiments of the invention include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program comprising program code for performing the method illustrated in the flow chart. In such an embodiment, the computer program may be downloaded and installed from a network through the communication section 609, and/or installed from the removable medium 611.
Computer-readable media, including both non-transitory and non-transitory, removable and non-removable media, may implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), Read Only Memory (ROM), Electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), Digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information that can be accessed by a computing device. As defined herein, a computer readable medium does not include a transitory computer readable medium such as a modulated data signal and a carrier wave.
For convenience of description, the above devices are described as being divided into various units by function, and are described separately. Of course, the functionality of the units may be implemented in one or more software and/or hardware when implementing the present application.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The application may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The application may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
The above description is only an example of the present application and is not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims (12)

1. A transient current calculation method for circulating current of a modular multilevel voltage source converter valve is characterized by comprising the following steps:
the method comprises the steps of collecting bridge arm currents and output currents of a modular multilevel converter, wherein the bridge arm currents comprise an upper bridge arm current and a lower bridge arm current;
determining a double-frequency component and a quadruple-frequency component of the circulating transient current according to inductance parameters of the coupling inductance, bridge arm current, output current, a second harmonic component formula and a fourth harmonic component formula, and further obtaining bridge arm circulating current;
and determining the reference voltage of the modular multilevel converter according to the bridge arm circulation current so as to inhibit the bridge arm circulation current.
2. The method for calculating the transient current circulating through the modular multilevel voltage source converter valve according to claim 1, further comprising the following steps before collecting the bridge arm current and the output current of the modular multilevel converter:
the coupling inductor is equivalent to a discrete inductor;
determining output voltages of an upper bridge arm and a lower bridge arm of an equivalent discrete inductance modular multilevel converter so as to obtain the output voltages of the bridge arms;
and performing Fourier expansion on the output voltage of the bridge arm to obtain a second harmonic component formula and a fourth harmonic component formula.
3. The method for calculating the transient current of the circulating current of the modular multilevel voltage source converter valve according to claim 2, wherein the equivalent of the coupling inductance to the discrete inductance specifically comprises:
determining the voltage drop of the coupling inductor according to the first sub-inductor, the second sub-inductor, the bridge arm current and the output current of the coupling inductor;
and the coupling inductor is equivalent to a discrete inductor according to the voltage drop of the coupling inductor.
4. The method for calculating the transient current of the circulating current of the modular multilevel voltage source converter valve according to claim 2, wherein the determining the output voltages of an upper bridge arm and a lower bridge arm of an equivalent discrete inductance modular multilevel converter to obtain the output voltages of the bridge arms specifically comprises:
determining the upper bridge arm current and the lower bridge arm current of the coupling inductor with the quadruple frequency components considered;
determining switching functions of an upper bridge arm and a lower bridge arm according to a preset switching function and performing Fourier expansion to obtain average currents of any capacitors of the upper bridge arm and the lower bridge arm of the modular multilevel converter;
performing Fourier expansion on the average current, and combining a capacitive reactance to obtain sub-module voltages of an upper bridge arm and a lower bridge arm;
and obtaining output voltages of the upper bridge arm and the lower bridge arm according to the sub-module voltage and the switching function, and further obtaining the output voltages of the bridge arms.
5. The method for calculating the transient current of the circulating current of the modular multilevel voltage source converter valve according to any one of claims 1 to 4, wherein the second harmonic component I2Formula and fourth harmonic component I4The formulas are respectively as follows:
Figure FDA0002475907120000021
wherein A and B are parameters,
Figure FDA0002475907120000022
representing the phase angle of the fundamental wave, N being the number of submodules in each bridge arm, omega being the angular frequency of the fundamental wave output by the converter, C being the capacitance of the submodule of the bridge arm, Leq＝L1+L2M, M represents the mutual inductance between the coupled inductors, L1Inductance value of the first sub-inductor of the coupling inductor, L2The inductance of the second sub-inductor for the coupling inductor, m represents the modulation ratio, IaIs expressed as ACEffective value of fundamental wave of side output current, IadIs the dc component in the bridge arm current.
6. A transient current calculation system for circulating current of a modular multilevel voltage source converter valve is characterized by comprising the following components:
the current acquisition module is used for acquiring bridge arm currents and output currents of the modular multilevel converter, wherein the bridge arm currents comprise an upper bridge arm current and a lower bridge arm current;
the loop current determining module is used for determining a frequency doubling component and a frequency quadrupling component of the loop current transient state current according to the inductance parameter of the coupling inductance, the bridge arm current, the output current, a second harmonic component formula and a fourth harmonic component formula and further obtaining the bridge arm loop current;
and the circulating current suppression module is used for determining the reference voltage of the modular multilevel converter according to the bridge arm circulating current so as to suppress the bridge arm circulating current.
7. The system for calculating the circulating current of the modular multilevel voltage source converter valve according to claim 6, further comprising a model establishing module for equating the coupling inductance to a discrete inductance, determining the output voltages of an upper bridge arm and a lower bridge arm of an equivalent discrete inductance modular multilevel converter, further obtaining the output voltages of the bridge arms, and performing Fourier expansion on the output voltages of the bridge arms to obtain a second harmonic component formula and a fourth harmonic component formula.
8. The system for calculating the transient current of the circulating current of the modular multilevel voltage source converter valve according to claim 7, wherein the model establishing module is specifically configured to determine the voltage drop of the coupling inductor according to the first sub-inductor, the second sub-inductor, the bridge arm current and the output current of the coupling inductor; and the coupling inductor is equivalent to a discrete inductor according to the voltage drop of the coupling inductor.
9. The system for calculating the circulating current transient state current of the modular multilevel voltage source converter valve according to claim 7, wherein the model establishing module is specifically configured to determine the upper bridge arm current and the lower bridge arm current of the coupling inductor considering the quadruple frequency component; determining switching functions of an upper bridge arm and a lower bridge arm according to a preset switching function and performing Fourier expansion to obtain average currents of any capacitors of the upper bridge arm and the lower bridge arm of the modular multilevel converter; performing Fourier expansion on the average current, and combining a capacitive reactance to obtain sub-module voltages of an upper bridge arm and a lower bridge arm; and obtaining output voltages of the upper bridge arm and the lower bridge arm according to the sub-module voltage and the switching function, and further obtaining the output voltages of the bridge arms.
10. The system of any one of claims 6-9, wherein the second harmonic component formula and the fourth harmonic component formula are respectively:
Figure FDA0002475907120000031
wherein A and B are parameters,
Figure FDA0002475907120000032
representing the phase angle of the fundamental wave, N being the number of submodules in each bridge arm, omega being the angular frequency of the fundamental wave output by the converter, C being the capacitance of the submodule of the bridge arm, Leq＝L1+L2M, M represents the mutual inductance between the coupled inductors, L1Inductance value of the first sub-inductor of the coupling inductor, L2The inductance of the second sub-inductor for the coupling inductor, m represents the modulation ratio, IaExpressed as the effective value of the fundamental wave of the output current on the AC side, IadIs the dc component in the bridge arm current.
11. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor,
the processor, when executing the program, implements the method of any of claims 1-5.
12. A computer-readable medium, having stored thereon a computer program,
the program when executed by a processor implementing the method according to any one of claims 1-5.
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Publication number Priority date Publication date Assignee Title
CN107465359A (en) * 2017-08-18 2017-12-12 北京能源集团有限责任公司 The circulation inhibition method and device of modularization multi-level converter
CN110011554A (en) * 2019-04-09 2019-07-12 上海电力学院 A kind of Modular multilevel converter loop current suppression device and method
CN110048582A (en) * 2019-05-23 2019-07-23 华北电力大学 A kind of MMC submodule capacitor voltage fluctuation suppressing method of Harmonic coupling injection

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107465359A (en) * 2017-08-18 2017-12-12 北京能源集团有限责任公司 The circulation inhibition method and device of modularization multi-level converter
CN110011554A (en) * 2019-04-09 2019-07-12 上海电力学院 A kind of Modular multilevel converter loop current suppression device and method
CN110048582A (en) * 2019-05-23 2019-07-23 华北电力大学 A kind of MMC submodule capacitor voltage fluctuation suppressing method of Harmonic coupling injection

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