CN107887923B - A kind of bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system - Google Patents
A kind of bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- 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
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- 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 present invention discloses a kind of bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system, is related to technical field of direct current power transmission, to solve the problems, such as that existing method cannot accurately calculate bipolar short-circuit current.The analysis method includes: to be latched the last stage in MMC, according to the electric discharge process of single-phase bridge arm Neutron module capacitor and the switching frequency of single-phase bridge arm Neutron module capacitor, constructs single-phase bridge arm Neutron module capacitor electric discharge frequency domain Type Equivalent Circuit Model；And according to the frequency domain Type Equivalent Circuit Model, single-phase bridge arm Neutron module capacitor electric discharge time-domain expression is obtained；In the stage after MMC locking, construct the frequency domain Type Equivalent Circuit Model of MMC topological structure；And according to the frequency domain Type Equivalent Circuit Model, the DC side electric current time-domain expression is obtained.The present invention is for calculating bipolar short-circuit current.
Description
Technical field
The present invention relates to technical field of direct current power transmission more particularly to a kind of bipolar short troubles of MMC-HVDC transmission system point
Analysis method.
Background technique
Modularization multi-level converter high voltage direct current (Modular Multilevel Converter Based High
Voltage Direct Current, referred to as MMC-HVDC) favorable expandability, output harmonic wave are small, switch because having for transmission system
The advantages such as frequency is low are paid close attention to by academia and engineering circles in recent years.Wherein, modularization multi-level converter MMC is usually by more
Identical submodule (Sub-module, the referred to as SM) cascade of a structure is constituted, the structure of submodule can be divided into half-H-bridge type,
Full H bridge type and double three kinds of clamped submodule types.The bridge arm of MMC is not only to execute the valve of switch motion, while being still connected to and changing
The controllable voltage source between device phase ac output end and DC bus is flowed, and submodule is the key that realize above-mentioned two function
Element.
However, in submodule handoff procedure, the current peak for flowing through submodule is much higher than due to the particularity of MMC structure
Virtual value, and current changing rate is higher.DC line damping additionally, due to MMC-HVDC transmission system is smaller, works as MMC-
When bipolar short trouble occurs on the DC line of HVDC transmission system, electric current is steeply risen, and voltage substantially falls, and is seriously threatened
The safety of MMC-HVDC transmission system.
Currently, although existing to the bipolar short trouble of MMC-HVDC transmission system more deep analysis and research, right
The considerations of influence of MMC control system and submodule switching change aspect after failure is not comprehensive enough, causes to transmit electricity as MMC-HVDC
After bipolar short trouble problem occurs in system, bipolar short-circuit current cannot be accurately calculated, influences MMC-HVDC transmission of electricity system
The safe and stable operation of system.
Summary of the invention
The purpose of the present invention is to provide a kind of bipolar analysis of Short Circuit Fault methods of MMC-HVDC transmission system, for improving
The precision of bipolar short-circuit current is calculated, the safe and stable operation for MMC-HVDC transmission system provides theoretical foundation.
To achieve the goals above, the invention provides the following technical scheme:
The present invention provides a kind of bipolar analysis of Short Circuit Fault methods of MMC-HVDC transmission system, comprising:
Step 10, it is latched the last stage in modularization multi-level converter MMC, according to putting for single-phase bridge arm Neutron module capacitor
The switching frequency of electric process and single-phase bridge arm Neutron module capacitor constructs single-phase bridge arm Neutron module capacitor electric discharge frequency domain etc.
It is worth circuit model；
Step 20, according to the single-phase bridge arm Neutron module capacitor electric discharge frequency domain Type Equivalent Circuit Model, single-phase bridge arm is obtained
Neutron module capacitor electric discharge time-domain expression；
Step 30, in the stage after MMC locking, the frequency domain Type Equivalent Circuit Model of MMC topological structure is constructed；
Step 40, according to the frequency domain Type Equivalent Circuit Model of the MMC topological structure, the expression of DC side electric current time domain is obtained
Formula.
Compared with prior art, the invention has the following beneficial effects:
In the present invention, according to the different stages of development of DC bipolar short trouble, by DC bipolar short trouble mechanism
Analysis can be divided into two stages: MMC is latched the stage after last stage and MMC locking, and it is corresponding to construct two stages
Type Equivalent Circuit Model is respectively used to after calculating bipolar short trouble generation, calculates the fault current of MMC locking front and back.And
During constructing Type Equivalent Circuit Model, sub-modular structure characteristic when having fully considered MMC-HVDC transmission system bipolar short trouble
And its influence of switching controlling mechanism, the equivalent capacitance calculation method in the case of submodule high frequency switching is proposed, and equivalent
The original state of capacitor determines method, so that the equivalence to sub- module capacitance is more accurate, closes to obtain more accurate MMC
The fault current for locking front and back, provides effective theoretical foundation for MMC-HVDC transmission system security and stability analysis.
Detailed description of the invention
The drawings described herein are used to provide a further understanding of the present invention, constitutes a part of the invention, this hair
Bright illustrative embodiments and their description are used to explain the present invention, and are not constituted improper limitations of the present invention.In the accompanying drawings:
Fig. 1 is MMC topology diagram in the embodiment of the present invention；
Fig. 2 is the flow chart of the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system in the embodiment of the present invention；
Time domain equivalent circuit figure when Fig. 3 is the single-phase bridge arm capacitor electric discharge of building of the embodiment of the present invention；
Fig. 4 is Fig. 3 Neutron module switching equivalent circuit diagram；
Frequency domain equivalent circuit diagram when Fig. 5 is the single-phase bridge arm capacitor electric discharge of building of the embodiment of the present invention；
Fig. 6 is the specific flow chart of step 20 in Fig. 2；
Fig. 7 is that MMC is latched preceding and t≤t0Frequency domain equivalent circuit diagram when Shi Danxiang bridge arm capacitor discharges；
Fig. 8 is MMC frequency domain equivalent circuit diagram after MMC locking；
Frequency domain equivalent circuit diagram when Fig. 9 is the three-phase bridge arm inductive discharge of building of the embodiment of the present invention.
Specific embodiment
For ease of understanding, with reference to the accompanying drawings of the specification, double to MMC-HVDC transmission system provided in an embodiment of the present invention
Extremely short road failure analysis methods are described in detail.
In existing MMC-HVDC transmission system, inverter first choice uses MMC, MMC to generally include three-phase bridge arm, three-phase
Frequency-modulated wave mutual deviation is hexagonal angle between bridge arm, to guarantee ac output voltage three-phase symmetrical.Every phase bridge arm include upper bridge arm and
Lower bridge arm, upper bridge arm and lower bridge arm are made of several submodules SM, and the submodule number of investment of every phase bridge arm any time
It is fixed, to maintain DC voltage constant.MMC fits desired ac output voltage by the investment of control submodule/cut out.
Illustratively, as shown in Figure 1, the circuit diagram is MMC topology diagram in the embodiment of the present invention, in this circuit diagram, UA、UB、UC
The respectively three-phase voltage of AC system, each mutually upper and lower bridge arm inductance value is L, resistance value R, and is connected with N number of capacitance
For the submodule of C, T in submodule1、T2For concatenated two insulated gate bipolar transistors (Insulate-Gate Bipolar
Transistor, referred to as IGBT), D1、D2For diode, wherein D1With T1Reverse parallel connection, D2With T2Reverse parallel connection；C is distribution
Capacitor, with T1、T2It is in parallel.When MMC-HVDC transmission system steady-state operation, MMC adjusts bridge arm electricity in each phase by switching submodule
Gesture UpkWith lower bridge arm potential Unk。
Referring to Fig. 2, the figure is the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system in the embodiment of the present invention
Flow chart.The bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system provided in an embodiment of the present invention includes:
Step 10, it is latched the last stage in modularization multi-level converter MMC, according to putting for single-phase bridge arm Neutron module capacitor
The switching frequency of electric process and single-phase bridge arm Neutron module capacitor constructs single-phase bridge arm Neutron module capacitor electric discharge frequency domain etc.
It is worth circuit model；
Step 20, according to single-phase bridge arm Neutron module capacitor electric discharge frequency domain Type Equivalent Circuit Model, single-phase bridge arm neutron is obtained
Module capacitance electric discharge time-domain expression；
Step 30, in the stage after MMC locking, the frequency domain Type Equivalent Circuit Model of MMC topological structure is constructed；
Step 40, according to the frequency domain Type Equivalent Circuit Model of the MMC topological structure, the expression of DC side electric current time domain is obtained
Formula.
When DC bipolar short trouble occurs for MMC-HVDC transmission system, DC bus-bar voltage is reduced to rapidly zero, above and below
The electric discharge of bridge arm submodule capacitor, causes DC bus current, bridge arm current to increase rapidly.When the Control protection system of MMC detects
To after DC bipolar short trouble, MMC is latched at once；After MMC locking, fault current gradually decays to zero.Therefore, in this hair
It, can be with by DC bipolar short trouble Analysis on Mechanism according to the different stages of development of DC bipolar short trouble in bright embodiment
Be divided into two stages: MMC is latched the stage after last stage and MMC locking, and constructs two stages corresponding equivalent circuit
Model is respectively used to after calculating bipolar short trouble generation, calculates the fault current of MMC locking front and back.And it is equivalent in building
During circuit model, sub-modular structure characteristic and its switching when having fully considered MMC-HVDC transmission system bipolar short trouble
The influence of controlling mechanism, propose equivalent capacitance calculation method in the case of submodule high frequency switching and equivalent capacitance just
Beginning state determines method, so that the equivalence to sub- module capacitance is more accurate, to obtain more accurate MMC locking front and back
Fault current provides effective theoretical foundation for MMC-HVDC transmission system security and stability analysis.
Since the control system of MMC has certain hysteresis characteristic, and MMC locking duration last stage is shorter, modulating wave
It can't substantially change in a short time, therefore before MMC locking, bipolar short trouble characteristic is influenced by control strategy
It is smaller.Therefore, in the present embodiment, the Type Equivalent Circuit Model that MMC is latched the last stage mainly considers the influences of two factors: one
It is that will not be reversed charging after sub-modular structure particularity causes submodule capacitor to discharge；Second is that the high frequency switching mistake of submodule
Journey.The former determines the structure of equivalent circuit, and the latter determines the parameter of equivalent circuit.
When above-mentioned steps 10 are embodied, step 10 is specifically included: the last stage is latched in MMC, according to MMC Neutron module
The electric discharge process of capacitor constructs single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit model；According to the single-phase bridge arm
The switching frequency of Neutron module capacitor electric discharge time domain equivalent circuit model and single-phase bridge arm Neutron module capacitor, calculates and obtains
Upper bridge arm equivalent capacitance, lower bridge arm equivalent capacitance, the initial voltage value of upper bridge arm equivalent capacitance and lower bridge arm of single-phase bridge arm etc.
It is worth the initial voltage value of capacitor；According to the upper bridge arm equivalent capacitance, lower bridge arm equivalent capacitance, upper bridge arm equivalent capacitance it is initial
The initial voltage value of voltage value and lower bridge arm equivalent capacitance, by the single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit
Model conversion is single-phase bridge arm Neutron module capacitor electric discharge frequency domain Type Equivalent Circuit Model.
Specifically, single-phase bridge arm neutron is constructed according to the electric discharge process of MMC Neutron module capacitor in the MMC locking last stage
Module capacitance electric discharge time domain equivalent circuit model.Due to being latched the last stage in MMC, the electric current that single-phase bridge arm upstream is crossed is mainly single
Phase bridge arm Neutron module capacitance discharge current.Equivalency transform can be carried out to circuit diagram shown in Fig. 1, form circuit diagram shown in Fig. 3, figure
3 be time domain equivalent circuit figure when the single-phase bridge arm capacitor that the embodiment of the present invention constructs discharges.C in Fig. 3pThe equivalent electricity of upper bridge arm
Capacitance, CnThe equivalent capacitance value of lower bridge arm, EpFor the both end voltage of upper bridge arm distribution capacity, EnIt is the two of lower bridge arm distribution capacity
Hold voltage, LeFor the equivalent inductance of single-phase bridge arm, ReThe substitutional resistance of single-phase bridge arm, T1-T4Respectively IGBT, trigger signal point
Not are as follows: T1=T3=1, T2=T4=0；D1-D4Respectively with the diode of corresponding IGBT reverse parallel connection.
Upper bridge arm potential UpkWith lower bridge arm potential UnkWhen lower, sufficiently high switching frequency is needed, to guarantee submodule electricity
The equilibrium for holding voltage, i.e., need to carry out the switching of multiple submodule under identical bridge arm potential.Illustratively, as shown in figure 4, figure
4 be Fig. 3 Neutron module switching equivalent circuit diagram.N in Fig. 4PIt is E for upper bridge arm potentialPWhen the bridge arm need the submodule that puts into
Number, NnIt is E for lower bridge arm potentialnWhen the bridge arm need the submodule number that puts into, N is bridge arm submodule sum, the bridge arm potential
Under, switch S1To switch SkWith fixed frequency rotation closure, k capacitor parallel connection, Mei Ge electricity are equivalent to when switching frequency is sufficiently high
Capacitance is C/Np。
Upper bridge arm equivalent capacitance CPWith lower bridge arm equivalent capacitance CnIt is respectively as follows:
The initial voltage value E of upper bridge arm equivalent capacitancep(0-) and lower bridge arm equivalent capacitance initial voltage value En(0-) meter
Formula is calculated to be respectively as follows:
Ep(0-)=Np*UCFormula (3)
En(0-)=Nn*UCFormula (4)
In above-mentioned formula (1), formula (2), formula (3) and formula (4), C is the capacitance of single-phase bridge arm, and N is single-phase
The number of bridge arm Neutron module, NPIt is E for upper bridge arm potentialPWhen this on bridge arm need the submodule number that puts into, NnFor lower bridge arm
Potential is EnWhen the lower bridge arm need the submodule number that puts into, UCFor the average voltage of single-phase bridge arm Neutron module capacitor.
Specifically, above-mentioned formula (3) and formula (4) can obtain with the following method:
Assuming that the average voltage level of each submodule capacitor is U in Fig. 1C, available single-phase according to law of conservation of energy
The equivalent voltage value at upper and lower bridge arm equivalent capacitance both ends in bridge arm, in single-phase bridge arm upper bridge arm submodule capacitor storage energy it
With with WpIt indicates and lower bridge arm submodule capacitor stores the sum of energy and uses WnIt indicates, WpAnd WnCalculating formula is respectively as follows:
As shown in figure 3, in the electric discharge of single-phase bridge arm submodule capacitor formula (7) can be used in time domain equivalent circuit diagram
With formula (8), the sum of bridge arm submodule capacitor storage energy W is calculated separatelyp' and lower bridge arm submodule capacitor storage energy
The sum of Wn', formula (7) and formula (8) are specific as follows:
It, can according to law of conservation of energy due to the equivalent circuit that Fig. 3 is single-phase bridge arm submodule capacitor electric discharge in Fig. 1
Know, WpAnd Wp' equal, WnAnd Wn' equal, that is, meet following formula (9) and formula (10):
Wp=W'pFormula (9)
Wn=W'nFormula (10)
Formula (5), formula (6), formula (7) and formula (8) are substituted into formula (9) and formula (10) respectively, can be acquired
The initial voltage value E of upper bridge arm equivalent capacitorp(0-) and lower bridge arm equivalent capacity initial voltage value En(0-), it is respectively as follows:
Ep(0-)=Np*UCFormula (3)
En(0-)=Nn*UCFormula (4)
The upper bridge arm equivalent capacitance C obtained according to above-mentioned calculatingp, lower bridge arm equivalent capacitance Cn, upper bridge arm equivalent capacitor just
Beginning voltage value Ep(0-) and lower bridge arm equivalent capacity initial voltage value En(0-), when discharging single-phase bridge arm capacitor shown in Fig. 3
Time domain equivalent circuit figure is converted, and frequency domain when can be obtained single-phase bridge arm Neutron module capacitor shown in fig. 5 electric discharge is equivalent
Circuit diagram.
In the above-described embodiments, the equivalent capacitance meter under identical bridge arm potential in the case of the high frequency switching of submodule is provided
Calculation method and the original state of equivalent capacitance determine method, so that the equivalence to sub- module capacitance is more accurate, are latched for direct current
The accurate calculating of the fault current of last stage provides basis.
Referring to Fig. 6, Fig. 6 is the specific flow chart of step 20 in Fig. 2.Above-mentioned steps 20 specifically comprise the following steps:
Step 21, in single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit model, when upper bridge arm equivalent capacitance
When being in discharge condition with lower bridge arm equivalent capacitance, equation is write according to voltage distribution law column:
In formula (11) and formula (12), UpIt (s) is upper bridge arm voltage, UnIt (s) is lower bridge arm voltage, LeFor bridge arm etc.
It is worth inductance, ReFor bridge arm substitutional resistance.
Step 22, according to above-mentioned formula (11) and formula (12), calculating can acquire bridge arm submodule capacitor both end voltage
Time domain mathematic(al) representation Up(t) and lower bridge arm submodule capacitor both end voltage time domain mathematic(al) representation Un(t):
Up(t)=L-1(Up(s)) formula (13)
Un(t)=L-1(Un(s)) formula (14)
Step 23, U is enabledp(t)=0 the time t that bridge arm submodule capacitor voltage drops to zero, is acquired1；Enable Un(t)=0,
Acquire the time t that lower bridge arm submodule capacitor voltage drops to zero2, when the submodule capacitor voltage of one of them half bridge arm declines
To after zero, due to diode (D2Or D4) clamping action, which, which is equivalent to, is short-circuited, and circuit structure changes, submodule
Block capacitor discharge process enters next stage, and the bridge arm that this time is first down to zero by submodule capacitor voltage determines, therefore logical
It crosses and compares t1And t2Size can obtain submodule capacitor electric discharge duration first stage t0:
t0=min (t1,t2) formula (15)
Min is to be minimized function in formula (15).
Step 24, when upper bridge arm submodule capacitor discharge time t and lower bridge arm submodule capacitor discharge time t be respectively less than etc.
In t0When, i.e. t≤t0When, son can be asked according to Kirchhoff's second law (Kirchhoff Voltage Laws, referred to as KVL)
Module capacitance discharge current frequency-domain expression:
Step 25, inverse Laplace transform is carried out to formula (16) and formula (17), can further acquires its submodule electricity
Discharge capacitor electric current time-domain expression:
i1(t)=L-1(I (s)) formula (18)
Step 26, as one in the voltage at upper bridge arm submodule capacitor both ends and the voltage at lower bridge arm submodule capacitor both ends
To after zero, submodule capacitor is occurred the tension discharge at a half bridge arm submodule capacitor both ends by lower shorted diode, circuit structure
Variation.Referring to Fig. 7, being latched preceding and t≤t for MMC0Shi Danxiang bridge arm capacitor electric discharge frequency domain equivalent circuit diagram.I (the t in Fig. 70)
For t0Moment bridge arm current value, Uk(t0) it is t0Moment is not discharged to zero submodule capacitor both end voltage value.It is acquired according to KVL
Submodule capacitance discharge current frequency-domain expression in Fig. 7:
Step 27, inverse Laplace transform is carried out to formula (19) and formula (20), can further acquires its submodule
Capacitance discharge current time-domain expression:
i2(t)=L-1(I (s)) formula (21)
In above-mentioned formula (11)-formula (21), L is the inductance value of single-phase bridge arm, LeFor the equivalent inductance of single-phase bridge arm,
ReFor the substitutional resistance of single-phase bridge arm, CkFor t0Moment is not discharged to zero bridge arm capacitor, and I (s) is the electric current of single-phase bridge arm, Up
It (s) is upper bridge arm voltage, UnIt (s) is lower bridge arm voltage, i (t0) it is t0Moment single-phase bridge arm current value, Uk(t0) it is t0Moment is not
It is discharged to zero submodule capacitor both end voltage value；S is the mathematic sign introduced in Laplace transform, and S=σ+j ω is multiple ginseng
Variable, also referred to as complex frequency.
After obtaining submodule capacitance discharge current time-domain expression formula (18) and formula (21), when MMC-HVDC is defeated
After bipolar short trouble occurs for electric system, (18) and formula (21) are utilized, MMC locking last stage submodule electricity can be accurately calculated
Discharge capacitor electric current provides effective theory to be latched the last stage in MMC for MMC-HVDC transmission system security and stability analysis
Foundation.
Referring to Fig. 8, Fig. 8 is MMC frequency domain equivalent circuit diagram after MMC locking.After MMC locking, MMC is in three phase full bridge not
Rectification state is controlled, all submodules are in bypass condition, and submodule capacitor stops electric discharge.KVL equation is write according to Fig. 8 column:
UB(s)-Lipb(0-)+Lipc(0-)-UC(s)=(Ipc-Ipb) * (R+sL) formula (22)
UA(s)+Lina(0-)-Linb(0-)-UB(s)=(Ina-Inb) * (R+sL) formula (23)
UB(s)+Linb(0-)-Linc(0-)-UC(s)=(Inb-Inc) * (R+sL) formula (24)
Lipa(0-)+Lina(0-)=(Ipa-Ina) * (R+sL) formula (25)
Ipa+Ipb+Ipc=IdcFormula (26)
DC side current frequency domain expression formula I can be found out by above equation groupdc(s), inverse Laplace transformation is further utilized
It can solve to obtain DC side electric current time-domain expression:
idc(t)=L-1(Idc(s)) formula (27)
In above-mentioned formula (22)-formula (27), UAIt (s) is A phase bridge arm voltage, UBIt (s) is B phase bridge arm voltage, UC(s)
For C phase bridge arm voltage, IdcIt (s) is the Frequency Domain Solution of DC side fault current, idcIt (t) is the time solution of DC side fault current,
Lipb(0-) it is bridge arm inductance initial voltage in B phase, Lipc(0-) it is bridge arm inductance initial voltage in C phase, Lina(0-) it is under A phase
Bridge arm inductance initial voltage, Linb(0-) it is B phase lower bridge arm inductance initial voltage, Linc(0-) it is that C phase lower bridge arm inductance is initially electric
Pressure, InaFor A phase lower bridge arm electric current, InbFor B phase lower bridge arm electric current, IncFor C phase lower bridge arm electric current, IpcFor bridge arm current in C phase,
IpbFor bridge arm current in A phase, IpaFor bridge arm current in A phase, R is the resistance value of single-phase bridge arm, and L is the resistance value of single-phase bridge arm.
After bipolar short trouble occurs for MMC-HVDC transmission system, in the stage after MMC locking, utilize (27) can be accurate
Stage DC side electric current after MMC is latched is calculated, thus the stage after MMC locking, for MMC-HVDC transmission system safety and stability point
Analysis provides effective theoretical foundation.
The submodule capacitance discharge current and DC side electric current obtained in order to ensure above-mentioned calculating is accurate, in above-described embodiment
On the basis of, the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system provided in an embodiment of the present invention further includes verifying as follows
Step, specific as follows:
In the stage after MMC locking, construct frequency domain Type Equivalent Circuit Model when three-phase bridge arm inductive discharge.Illustratively, it asks
Frequency domain equivalent circuit diagram when refering to the three-phase bridge arm inductive discharge that Fig. 9, Fig. 9 are building of the embodiment of the present invention.In Fig. 9, Cpk
And CnkThe respectively equivalent capacitance of upper and lower bridge arm, Epk(0-) and Enk(0-) be respectively upper and lower bridge arm equivalent capacitance initial voltage
Value, ik(0-) it is each phase bridge arm initial current value, LeFor each bridge arm equivalent inductance, ReFor bridge arm substitutional resistance.
Frequency domain Type Equivalent Circuit Model when according to three-phase bridge arm inductive discharge, and bridge arm inductive discharge is write according to KVL column
The math equation of electric current:
Laplace transform is carried out to formula (28) and formula (29), obtains DC side fault current time-domain expression:
Idc(t)=L-1(Idc(s)) formula (30)
According to formula (30), it can calculate and acquire Ia(s)、Ib(s) and Ic(s), to obtain each phase submodule capacitor both ends electricity
Press frequency-domain expression:
Using inverse Laplace transform, each phase capacitance terminal voltage its time domain can be solved to obtain from formula (31) and formula (32)
Expression formula:
UpK (t)=L-1(Upk(s)) formula (33)
Unk(t)=L-1(Unk(s)) formula (34)
It enables each phase capacitor both end voltage be equal to zero, acquires each voltage over zero time t1-t6, by comparing t1-t6It is big
It is small, it can be in the hope of duration first stage t0。
t0=min (t1,t2,t3,t4,t5,t6) formula (35)
Compare t0With converter blocking time tblockSize, if t0≥tblock, then calculating terminates；t0<tblock, then electricity is enabled
Hold the capacitance short-circuit that voltage drops to zero, frequency domain circuit model rebuild according to each bridge arm current and each phase capacitance terminal voltage,
Carry out the calculating of next stage, and so on, it can be in the hope of each stage DC side discharge current.
In above-mentioned formula (28)-formula (35), CpkFor upper bridge arm equivalent capacitance, CnkFor lower bridge arm equivalent capacitance, Epk
(0-) be upper bridge arm equivalent capacitance initial voltage value, Enk(0-) be lower bridge arm equivalent capacitance initial voltage value, ik(0-) it is each
Phase bridge arm initial current value, LeFor the equivalent inductance of single-phase bridge arm, ReFor the substitutional resistance of single-phase bridge arm.
The above description is merely a specific embodiment, but scope of protection of the present invention is not limited thereto, any
Those familiar with the art in the technical scope disclosed by the present invention, can easily think of the change or the replacement, and should all contain
Lid is within protection scope of the present invention.Therefore, protection scope of the present invention should be based on the protection scope of the described claims.
Claims (7)
1. a kind of bipolar analysis of Short Circuit Fault method of modularization multi-level converter high voltage direct current MMC-HVDC transmission system, special
Sign is, comprising:
Step 10, modularization multi-level converter MMC be latched the last stage, according to the electric discharge of single-phase bridge arm Neutron module capacitor into
The switching frequency of journey and single-phase bridge arm Neutron module capacitor constructs the single-phase equivalent electricity of bridge arm Neutron module capacitor electric discharge frequency domain
Road model；
Step 20, according to the single-phase bridge arm Neutron module capacitor electric discharge frequency domain Type Equivalent Circuit Model, single-phase bridge arm neutron is obtained
Module capacitance electric discharge time-domain expression；
Step 30, in the stage after MMC locking, the frequency domain Type Equivalent Circuit Model of MMC topological structure is constructed；
Step 40, according to the frequency domain Type Equivalent Circuit Model of the MMC topological structure, DC side electric current time-domain expression is obtained.
2. the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system according to claim 1, which is characterized in that described
Step 10 includes:
It constructs single-phase bridge arm Neutron module capacitor according to the electric discharge process of MMC Neutron module capacitor in the MMC locking last stage and puts
Electric time domain equivalent circuit model；
According to the single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit model and single-phase bridge arm Neutron module capacitor
Switching frequency, calculate the upper bridge arm equivalent capacitance for obtaining single-phase bridge arm, lower bridge arm equivalent capacitance, upper bridge arm equivalent capacitance just
The initial voltage value of beginning voltage value and lower bridge arm equivalent capacitance；
According to the initial voltage value and lower bridge arm of the upper bridge arm equivalent capacitance, lower bridge arm equivalent capacitance, upper bridge arm equivalent capacitance
The single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit model conversion is single-phase by the initial voltage value of equivalent capacitance
Bridge arm Neutron module capacitor electric discharge frequency domain Type Equivalent Circuit Model.
3. the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system according to claim 2, which is characterized in that
The upper bridge arm equivalent capacitance C of the single-phase bridge armpWith lower bridge arm equivalent capacitance CnCalculation formula be respectively as follows:
The initial voltage value E of the upper bridge arm equivalent capacitancep(0-) and lower bridge arm equivalent capacitance initial voltage value En(0-) meter
Formula is calculated to be respectively as follows:
Ep(0-)=Np*UCFormula (3)
En(0-)=Nn*UCFormula (4)
Wherein, C is the capacitance of single-phase bridge arm, and N is the number of single-phase bridge arm Neutron module, NPIt is E for upper bridge arm potentialPWhen should
Upper bridge arm needs the submodule number put into, NnIt is E for lower bridge arm potentialnWhen the lower bridge arm need the submodule number that puts into, UC
For the average voltage of single-phase bridge arm Neutron module capacitor.
4. the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system according to claim 3, which is characterized in that use
Following method obtains formula (3) and formula (4):
Assuming that the average voltage of single-phase bridge arm Neutron module capacitor is U in MMC topological structureC, then the upper bridge arm submodule of single-phase bridge arm
Block capacitor stores energy WpEnergy W is stored with lower bridge arm submodule capacitornIt is respectively as follows:
In single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit model, upper bridge arm submodule capacitor stores energy Wp' and under
Bridge arm submodule capacitor stores energy Wn' be respectively as follows:
According to law of conservation of energy:
Wp=W 'pFormula (9)
Wn=W 'nFormula (10)
Formula (5), formula (6), formula (7) and formula (8) are substituted into formula (9) and formula (10), calculates and obtains formula (3)
With formula (4).
5. the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system according to claim 1, which is characterized in that described
Step 20 includes:
Step 21, in single-phase bridge arm Neutron module capacitor electric discharge time domain equivalent circuit model, when upper bridge arm equivalent capacitance is under
When bridge arm equivalent capacitance is in discharge condition, formula (11) and formula (12) are write according to voltage distribution law column:
Step 22, according to formula (11) and formula (12), bridge arm capacitor both end voltage U in acquisitionp(t) and lower bridge arm capacitor both ends
Voltage Un(t) time domain mathematic(al) representation:
Up(t)=L-1(Up(s)) formula (13)
Un(t)=L-1(Un(s)) formula (14)
Step 23, U is enabledp(t)=0 the time t that bridge arm capacitor both end voltage drops to zero, is acquired1, enable Un(t)=0 it, acquires down
Bridge arm capacitor both end voltage drops to zero time t2, obtain the duration t of bridge arm capacitor electric discharge0:
t0=min (t1,t2) formula (15)
Step 24, it is equal to t when upper bridge arm capacitor discharge time t and lower bridge arm capacitor discharge time t is respectively less than0When, suddenly according to Kiel
The frequency-domain expression formula (16) and formula (17) of husband's voltage law acquisition bridge arm capacitance discharge current:
Step 25, inverse Laplace transform is carried out to formula (16) and formula (17), obtains the time domain of bridge arm capacitance discharge current
Expression formula:
i1(t)=L-1(I (s)) formula (18)
Step 26, when a bridge arm capacitor in upper bridge arm capacitor and lower bridge arm capacitor is discharged to zero, according to kirchhoff electricity
Law is pressed to obtain the frequency-domain expression formula (19) and formula (20) of bridge arm capacitance discharge current:
Step 27, inverse Laplace transform is carried out to formula (19) and formula (20), obtains the time domain of bridge arm capacitance discharge current
Expression formula:
i2(t)=L-1(I (s)) formula (21)
Wherein, L is the inductance value of single-phase bridge arm, LeFor the equivalent inductance of single-phase bridge arm, ReFor the substitutional resistance of single-phase bridge arm, Ck
For t0Moment is not discharged to zero bridge arm capacitor, and I (s) is the electric current of single-phase bridge arm, UpIt (s) is upper bridge arm voltage, Un(s) under being
Bridge arm voltage, i (t0) it is t0Moment single-phase bridge arm current value, Uk(t0) it is t0Moment is not discharged to zero submodule capacitor both ends electricity
Pressure value, CpFor the upper bridge arm equivalent capacitance of single-phase bridge arm, CnFor the lower bridge arm equivalent capacitance of single-phase bridge arm, Ep(0-) it is upper bridge arm
The initial voltage value of equivalent capacitance, En(0-) is the initial voltage value of lower bridge arm equivalent capacitance.
6. the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system according to claim 1, which is characterized in that described
Step 40 includes:
Equation is write according to the frequency domain Type Equivalent Circuit Model and Kirchhoff's second law of MMC topological structure column:
UB(s)-Lipb(0-)+Lipc(0-)-UC(s)=(Ipc-Ipb) * (R+sL) formula (22)
UA(s)+Lina(0-)-Linb(0-)-UB(s)=(Ina-Inb) * (R+sL) formula (23)
UB(s)+Linb(0-)-Linc(0-)-UC(s)=(Inb-Inc) * (R+sL) formula (24)
Lipa(0-)+Lina(0-)=(Ipa-Ina) * (R+sL) formula (25)
Ipa+Ipb+Ipc=IdcFormula (26)
According to formula (22), formula (23), formula (24), formula (25) and formula (26), DC side fault current frequency domain is obtained
Expression formula Idc(s)；
To DC side fault current frequency domain presentation Formulas Idc(s) inverse Laplace transformation is carried out, when asking to obtain DC side fault current
Domain expression formula:
idc(t)=L-1(Idc(s)) formula (27)
Wherein, UAIt (s) is A phase bridge arm voltage, UBIt (s) is B phase bridge arm voltage, UCIt (s) is C phase bridge arm voltage, IdcIt (s) is direct current
The Frequency Domain Solution of side fault current, idcIt (t) is the time solution of DC side fault current, Lipa(0-) it is that bridge arm inductance is initially electric in A phase
Pressure, Lipb(0-) it is bridge arm inductance initial voltage in B phase, Lipc(0-) it is bridge arm inductance initial voltage in C phase, Lina(0-) it is A phase
Lower bridge arm inductance initial voltage, Linb(0-) it is B phase lower bridge arm inductance initial voltage, Linc(0-) it is that C phase lower bridge arm inductance is initial
Voltage, InaFor A phase lower bridge arm electric current, InbFor B phase lower bridge arm electric current, IncFor C phase lower bridge arm electric current, IpcFor bridge arm electricity in C phase
Stream, IpbFor bridge arm current in B phase, IpaFor bridge arm current in A phase, R is the resistance value of single-phase bridge arm, and L is the resistance of single-phase bridge arm
Value.
7. the bipolar analysis of Short Circuit Fault method of MMC-HVDC transmission system according to claim 1, which is characterized in that described
The bipolar analysis of Short Circuit Fault method of MMC-HVDV transmission system further include:
In the stage after MMC locking, construct frequency domain Type Equivalent Circuit Model when three-phase bridge arm inductive discharge；
Frequency domain Type Equivalent Circuit Model and Kirchhoff's second law when according to three-phase bridge arm inductive discharge obtain bridge arm inductance
The frequency-domain expression of discharge current:
Laplace transform is carried out to formula (22) and formula (23), obtains DC side fault current time-domain expression:
Idc(t)=L-1(Idc(s)) formula (30)
According to formula (30), each phase submodule capacitor both end voltage frequency-domain expression is obtained:
Inverse Laplace transform is carried out to formula (31) and formula (32), obtains each phase submodule capacitor both end voltage time domain expression
Formula:
Upk(t)=L-1(Upk(s)) formula (33)
Unk(t)=L-1(Unk(s)) formula (34)
Enable Upk(t)=0 each phase submodule capacitor both end voltage zero crossing time t, is acquired1-t6, obtain holding for bridge arm inductive discharge
Continuous time t0:
t0=min (t1,t2,t3,t4,t5,t6) formula (35)
Compare t0With converter blocking time tblockSize, if t0≥tblock, then calculating terminates；t0<tblock, then submodule is enabled
Capacitance voltage drops to zero capacitance short-circuit, and rebuilds frequency according to each bridge arm current and each phase submodule capacitor both end voltage
Domain circuit model recalculates DC side electric current, and so on, acquire the DC side electric discharge in bridge arm inductive discharge each stage
Electric current；
Wherein, CpkFor upper bridge arm equivalent capacitance, CnkFor lower bridge arm equivalent capacitance, Epk(0-) is the initial of upper bridge arm equivalent capacitance
Voltage value, Enk(0-) is the initial voltage value of lower bridge arm equivalent capacitance, ik(0-) is each phase bridge arm initial current value, LeIt is single-phase
The equivalent inductance of bridge arm, ReFor the substitutional resistance of single-phase bridge arm, CpFor the upper bridge arm equivalent capacitance of single-phase bridge arm, CnFor single-phase bridge
The lower bridge arm equivalent capacitance of arm, Ep(0-) be upper bridge arm equivalent capacitance initial voltage value, En(0-) it is lower bridge arm equivalent capacitance
Initial voltage value, IkFor bridge arm inductive discharge electric current, IdcFor DC side fault current.
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| CN109038502B (en) * | 2018-08-21 | 2019-10-22 | 广东电网有限责任公司 | A kind of low-voltage overcurrent protection setting method, device, equipment and storage medium |
| CN109117567B (en) * | 2018-08-24 | 2023-04-21 | 武汉大学 | MMC discrete modeling-based DC side short-circuit current calculation method |
| CN109638789B (en) * | 2018-10-29 | 2020-07-07 | 全球能源互联网研究院有限公司 | Direct-current bipolar short-circuit fault protection method and device of flexible alternating-current and direct-current interconnection system |
| CN110175351B (en) * | 2019-04-15 | 2023-02-28 | 南方电网科学研究院有限责任公司 | Converter transformer modeling method |
| CN110108986A (en) * | 2019-05-29 | 2019-08-09 | 华北电力大学 | DC grid fault current complex frequency domain calculation method |
| CN110350505B (en) * | 2019-07-15 | 2020-10-27 | 贵州电网有限责任公司 | Control method for inhibiting direct-current voltage fluctuation during flexible direct-current power transmission power adjustment |
| CN110729746B (en) * | 2019-09-09 | 2020-09-25 | 中国南方电网有限责任公司超高压输电公司昆明局 | Direct current transmission converter ground fault positioning method |
| CN113051707B (en) * | 2021-02-02 | 2023-08-18 | 山东大学 | Method and system for analyzing contribution short-circuit current of converter station at alternating current bus |
| CN113922408B (en) * | 2021-09-30 | 2023-12-08 | 合肥工业大学 | MMC-HVDC power grid bipolar short-circuit fault current calculation method based on parameter inversion |
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