CN107863758A - The improved method of MMC DC voltages protection - Google Patents

The improved method of MMC DC voltages protection Download PDF

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Publication number
CN107863758A
CN107863758A CN201610952993.1A CN201610952993A CN107863758A CN 107863758 A CN107863758 A CN 107863758A CN 201610952993 A CN201610952993 A CN 201610952993A CN 107863758 A CN107863758 A CN 107863758A
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msub
mrow
voltage
protection
mmc
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CN107863758B (en
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李国庆
娄剑
王鹤
王振浩
于华楠
刘芮彤
杨滢璇
韩子娇
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State Power Research Institute Of Liaoning Electric Power Co
State Grid Corp of China SGCC
Northeast Electric Power University
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State Power Research Institute Of Liaoning Electric Power Co
State Grid Corp of China SGCC
Northeast Dianli University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems

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  • Emergency Protection Circuit Devices (AREA)
  • Inverter Devices (AREA)

Abstract

A kind of improved method of MMC DC voltages protection, belongs to technical field of HVDC transmission.The purpose of the present invention is to be used as the locking criterion of DC voltage protection by voltage of increasing exchanges, to realize the improved method for the MMC DC voltages protection for solving direct current protecting maloperation.Step of the present invention is the locking criterion for determining DC voltage protection by carrying out qualitative analysis to MMC HVDC system mathematic models, determines alternating voltage setting valve U in DC voltage protectionac_set, improve DC voltage protection.The present invention on the basis of MMC HVDC mathematical modelings deepens, further to MMC HVDC fault in ac transmission system when direct current protecting configuration carry out in depth study there is obvious engineering application value and realistic meaning.

Description

The improved method of MMC DC voltages protection
Technical field
The invention belongs to technical field of HVDC transmission.
Background technology
High voltage dc transmission technology based on modularization multi-level converter（MMC-HVDC）As a kind of new flexibility HVDC Transmission Technology, search time is shorter, and practical engineering application is deficienter, it is necessary to be furtherd investigate to the technology.Currently may be used Documents and materials for reference primarily focus on the stable state control mechanism such as the modeling and simulating of MMC-HVDC systems, modulation strategy, for The research also accident analyses for focusing on DC side in terms of protection more.In modular multilevel high pressure flexible direct current transmission system In, protection is respectively configured with straight-flow system in AC system.When straight-flow system breaks down, direct current protecting cuts off rapidly failure, To ensure DC equipment from damage；Similarly, harmonics work rapidly after AC system breaks down, while direct current protecting It should be failure to actuate.But direct current transient state and DC Line Fault caused by AC fault have similitude, and direct current protecting is former Reason has imperfection with setting method, and AC fault may cause direct current protecting malfunction when occurring.According to flexible DC power transmission From the point of view of the situation of engineering site feedback, when AC fault occurs, the accident of direct current protecting malfunction happens occasionally, to the safety of system Operation causes threat.Therefore, on the basis of MMC-HVDC mathematical modelings are deepened, further to the event of MMC-HVDC AC systems Direct current protecting configuration during barrier, which carries out in depth research, has obvious engineering application value and realistic meaning.
The content of the invention
The purpose of the present invention is to be used as the locking criterion of DC voltage protection by voltage of increasing exchanges, and is solved directly to realize Flow the improved method of the MMC DC voltages protection of false protection accident.
Step of the present invention is：
Step 1：The locking criterion for determining DC voltage protection by carrying out qualitative analysis to MMC-HVDC system mathematic models：
Step 1-1：MMC ac circuit equivalent equations can be obtained according to Kirchhoff's law：
Formula（1）In：Wherein ujFor alternating voltage, ijFor alternating current, upj、unjThe respectively upper and lower bridge arm voltage of j phases, udcTo be straight Flow voltage, L0For bridge arm inductance, R0For arm resistance, j=a, b, c,It is to alternating current ijDifferential；
Step 1-2：According to formula（1）Derive DC voltage udcEquivalent equation formula：
Step 1-3：Analyzed according to circuit theory, obtain the total capacitance voltage equation of upper and lower bridge arm input：
Wherein ujFor alternating voltage, udiffjFor unbalance voltage drop inside jth phase；
Step 1-4：According to above-mentioned formula（2）, derive that MMC-HVDC occurs to cause DC voltage u during AC failuredcDecline While three-phase alternating voltage virtual value also reduce, but DC Line Fault will not cause alternating voltage virtual value to reduce, therefore carry Go out the locking criterion for protecting alternating voltage as DC voltage, when alternating voltage is less than setting valve DC voltage protection blocking；
Step 2：Determine alternating voltage setting valve U in DC voltage protectionac_set, improve DC voltage protection：
Step 2-1：Calculate and compare MMC-HVDC and occur to include single-phase grounding fault, two-phase short-circuit fault, two phase ground Alternating voltage virtual value during AC fault including short trouble, three phase short circuit fault, choose wherein maximum Uacmax1；
Step 2-2：Alternating voltage is unaffected when MMC-HVDC generation DC sides break down, and is AC system output voltage Uac2；
Step 2-3：Choose alternating voltage setting valve Uac_set, wherein
Step 2-4：Alternating voltage setting valve U is introduced in the protection of MMC-HVDC DC voltagesac_set, measurement alternating voltage Uac, Work as Uac＜ Uac_setWhen DC voltage protection blocking, solve the problems, such as that AC fault easily causes DC voltage false protection.
The present invention builds MMC-HVDC simulation models in PSCAD/EMTDC emulation platforms, its verification method:
Step 3-1：Mathematical modeling is built, builds the MMC-HVDC both-ends system of 11 level in PSCAD/EMTDC on this basis System simulation model, and commonly use protection for the soft straight engineering such as the protection of system configuration DC voltage, alternating voltage protection；
Step 3-2：MMC-HVDC double ended systems simulation model include single-phase grounding fault, two-phase short-circuit fault, AC fault emulation including two-phase short circuit and ground fault, three phase short circuit fault, trouble point is arranged on transformer primary side, failure After generation DC voltage protection is there occurs malfunction, therefore simulation results show AC fault can cause DC voltage protection to miss It is dynamic；
Step 3-3：Increase exchanges the locking criterion that voltage is protected as DC voltage, i.e., increase a comparison in simulation model Logic, when actual alternating voltage is less than alternating voltage setting valve, by DC voltage protection blocking, simulation result shows that this is changed Enter measure and effectively avoid the situation that DC Line Fault causes alternating voltage false protection, demonstrate the improved method have it is feasible Property.
In step 2-1 of the present invention during singlephase earth fault：Alternating voltage virtual value is calculated, using A phases as failure phase, i.e. UA= 0, non-faulting phase voltage formula is calculated as follows：
E in formulaAIt is failure phase-to-ground voltage, Z0、Z1、Z2It is the zero sequence, positive sequence, negative sequence impedance entered from the point of view of failure,It is complex factor.When singlephase earth fault occurs, Uacmax1=UB=UC。
The present invention on the basis of MMC-HVDC mathematical modelings are deepened, further to MMC-HVDC fault in ac transmission system when Direct current protecting configuration, which carries out in depth research, has obvious engineering application value and realistic meaning.
The present invention systematically analyzes friendship using the transient response of direct current protecting under MMC-HVDC fault in ac transmission system as point of penetration Streaming system failure influences to caused by direct current protecting, combs out the several straight of frequent configuration in compliance DC transmission engineering Protected mode is flowed, and proposes three phase short circuit fault and causes the mechanism of DC voltage false protection and be correspondingly improved measure, Reliability for further lifting DC system protection provides guidance.
The improved method of DC voltage protection provided by the invention solves fault in ac transmission system and caused directly to a certain extent The problem of flowing voltage protection malfunction, has promotional value.
Brief description of the drawings
Fig. 1 is the mono- station system topological figures of MMC-HVDC；
Fig. 2 is MMC AC singlephase earth fault equivalent circuit diagrams；
Fig. 3 is MMC AC double earthfault equivalent circuit diagrams；
Fig. 4 is MMC AC three-phase ground failure equivalent circuit diagrams；
Alternating voltage waveform figure when Fig. 5 is three phase short circuit fault；
Alternating voltage waveform figure when Fig. 6 is direct current disconnection fault；
Fig. 7 is MMC-HVDC relaying configuration figures；
Fig. 8 is the protection illustraton of model after improving；
DC voltage waveform figure when Fig. 9 is three phase short circuit fault（Rectification side constant DC voltage control）；
DC voltage waveform figure when Figure 10 is three phase short circuit fault（Inverter side constant DC voltage control）.
Embodiment
Direct current transient state and DC Line Fault of the invention caused by AC fault have similitude, and direct current protecting principle There is imperfection with setting method, AC fault may cause direct current protecting malfunction when occurring.According to flexible DC power transmission work From the point of view of the situation of journey scene feedback, when AC fault occurs, the accident of direct current protecting malfunction is happened occasionally, and the safety of system is transported Row causes threat.
In order to solve the above-mentioned technical problem, the present invention proposes a kind of improved MMC DC voltages Protection criteria, main contents It is the locking criterion that voltage is protected as DC voltage of increasing exchanges.
Methods described comprises the steps：
1st, a kind of method improved MMC DC voltages by increasing locking criterion and protected, voltage of to the effect that increasing exchanges are made For the locking criterion of DC voltage protection, it is characterized in can avoiding in fault in ac transmission system hindering characteristic similarity for some reason and causes False protection.Methods described comprises the steps：
Step 1：The locking criterion for determining DC voltage protection by carrying out qualitative analysis to MMC-HVDC system mathematic models.
Step 1-1：MMC ac circuit equivalent equations can be obtained according to Kirchhoff's law：
Formula（1）In：Wherein ujFor alternating voltage, ijFor alternating current, upj、unjThe respectively upper and lower bridge arm voltage of j phases, udcTo be straight Flow voltage, L0For bridge arm inductance, R0For arm resistance,It is to alternating current ijDifferential.
Step 1-2：According to formula（1）Derive DC voltage udcEquivalent equation formula：
Step 1-3：Analyzed according to circuit theory, obtain the total capacitance voltage equation of upper and lower bridge arm input：
Wherein ujFor alternating voltage, udiffjFor unbalance voltage drop inside jth phase.
Step 1-4：According to above-mentioned formula（2）, derive that MMC-HVDC occurs to cause DC voltage u during AC failuredc Three-phase alternating voltage virtual value also reduces while decline, but DC Line Fault will not cause alternating voltage virtual value to reduce, because The locking criterion that this proposition protects alternating voltage as DC voltage, when alternating voltage closes less than the protection of setting valve DC voltage Lock.
Step 2：Determine alternating voltage setting valve U in DC voltage protectionac_set, improve DC voltage protection.
Step 2-1：Calculate and compare MMC-HVDC and occur to include single-phase grounding fault, two-phase short-circuit fault, two-phase Alternating voltage virtual value during AC fault including ground short circuit failure, three phase short circuit fault, choose wherein maximum Uacmax1。
By taking singlephase earth fault as an example, alternating voltage virtual value is calculated, using A phases as failure phase, i.e. UA=0, non-faulting is mutually electric Pressure formula is calculated as follows：
E in formulaAIt is failure phase-to-ground voltage, Z0、Z1、Z2It is the zero sequence, positive sequence, negative sequence impedance entered from the point of view of failure,It is complex factor.When singlephase earth fault occurs, Uacmax1=UB=UC.Handed over during generation other types failure The computational methods of stream voltage no longer repeat one by one.
Step 2-2：Alternating voltage is unaffected when MMC-HVDC generation DC sides break down, for AC system output electricity Press Uac2。
Step 2-3：Choose alternating voltage setting valve Uac_set, wherein
Step 2-4：Alternating voltage setting valve U is introduced in the protection of MMC-HVDC DC voltagesac_set, measure alternating voltage Uac, work as Uac＜ Uac_setWhen DC voltage protection blocking, solve AC fault and easily cause asking for DC voltage false protection Topic.
Step 3：:MMC-HVDC simulation models are built in PSCAD/EMTDC emulation platforms, that verifies proposed method can Row.
Step 3-1：Mathematical modeling is built, the MMC-HVDC for building 11 level in PSCAD/EMTDC on this basis is double End system simulation model, and be the soft straight conventional protection of engineering such as the protection of system configuration DC voltage, alternating voltage protection.
Step 3-2：MMC-HVDC double ended systems simulation model is carried out to include single-phase grounding fault, line to line fault event AC fault emulation including barrier, two-phase short circuit and ground fault, three phase short circuit fault, trouble point are arranged on transformer primary side, After failure occurs DC voltage protection is there occurs malfunction, therefore simulation results show AC fault can cause DC voltage to be protected Malfunction.
Step 3-3：Increase exchanges the locking criterion that voltage is protected as DC voltage, i.e., increase by one in simulation model CL Compare Logic, when actual alternating voltage is less than alternating voltage setting valve, by DC voltage protection blocking, simulation result shows this One corrective measure effectively avoids the situation that DC Line Fault causes alternating voltage false protection, and demonstrating the improved method has Feasibility.
The embodiment of the present invention is described in further detail below in conjunction with the accompanying drawings：
1st, a kind of improved method of MMC DC voltages protection, to the effect that increases exchanges what voltage was protected as DC voltage Locking criterion, it is characterized in avoid hindering false protection caused by characteristic similarity for some reason in fault in ac transmission system.
Methods described comprises the steps：
1st, a kind of method improved MMC DC voltages by increasing locking criterion and protected, voltage of to the effect that increasing exchanges are made For the locking criterion of DC voltage protection, it is characterized in can avoiding in fault in ac transmission system hindering characteristic similarity for some reason and causes False protection.Methods described comprises the steps：
Step 1：The locking criterion for determining DC voltage protection by carrying out qualitative analysis to MMC-HVDC system mathematic models.
Step 1-1：It is as shown in Figure 1 the mono- station system topological figures of MMC-HVDC, MMC exchanges can be obtained according to Kirchhoff's law Loop equivalent equation：
Formula（1）In：Wherein ujFor alternating voltage, ijFor alternating current, upj、unjThe respectively upper and lower bridge arm voltage of j phases, udcTo be straight Flow voltage, L0For bridge arm inductance, R0For arm resistance, j=a, b, c,It is to alternating current ijDifferential.
Step 1-2：According to formula（1）Derive DC voltage udcEquivalent equation formula：
Step 1-3：Analyzed according to circuit theory, obtain the total capacitance voltage equation of upper and lower bridge arm input：
Wherein ujFor alternating voltage, udiffjFor unbalance voltage drop inside jth phase.
Step 1-4：According to above-mentioned formula（2）, derive that MMC-HVDC occurs to cause DC voltage u during AC failuredc Three-phase alternating voltage virtual value also reduces while decline, but DC Line Fault will not cause alternating voltage virtual value to reduce, because The locking criterion that this proposition protects alternating voltage as DC voltage, when alternating voltage closes less than the protection of setting valve DC voltage Lock.
Step 2：Determine alternating voltage setting valve U in DC voltage protectionac_set, improve DC voltage protection.
Step 2-1：Calculate and compare MMC-HVDC and occur to include single-phase grounding fault, two-phase short-circuit fault, two-phase Alternating voltage virtual value during AC fault including ground short circuit failure, three phase short circuit fault, failure equivalent circuit diagram such as Fig. 2, Shown in Fig. 3, Fig. 4, wherein maximum U is chosenacmax1.As shown in Figure 5.
By taking singlephase earth fault as an example, alternating voltage virtual value is calculated, using A phases as failure phase, i.e. UA=0, non-faulting is mutually electric Pressure formula is calculated as follows：
E in formulaAIt is failure phase-to-ground voltage, Z0、Z1、Z2It is the zero sequence, positive sequence, negative sequence impedance entered from the point of view of failure,It is complex factor.When singlephase earth fault occurs, Uacmax1=UB=UC.Handed over during generation other types failure The computational methods of stream voltage no longer repeat one by one.
Step 2-2：Alternating voltage is unaffected when MMC-HVDC generation DC sides break down, for AC system output electricity Press Uac2.As shown in Figure 6.
Step 2-3：Choose alternating voltage setting valve Uac_set, wherein
Step 2-4：Alternating voltage setting valve U is introduced in the protection of MMC-HVDC DC voltagesac_set, measurement alternating voltage Uac, Work as Uac＜ Uac_setWhen DC voltage protection blocking, solve the problems, such as that AC fault easily causes DC voltage false protection.It is soft The protection that property DC transmission engineering direct current place mainly configures is as shown in Figure 7.
Step 3：:MMC-HVDC simulation models are built in PSCAD/EMTDC emulation platforms, that verifies proposed method can Row.
Step 3-1：Mathematical modeling is built, the MMC-HVDC for building 11 level in PSCAD/EMTDC on this basis is double End system simulation model, and be the soft straight conventional protection of engineering such as the protection of system configuration DC voltage, alternating voltage protection.Emulation system Major parameter of uniting is as shown in table 1.
Table 1
Step 3-2：MMC-HVDC double ended systems simulation model include single-phase grounding fault, two-phase short-circuit fault, AC fault emulation including two-phase short circuit and ground fault, three phase short circuit fault, trouble point is arranged on transformer primary side, failure After generation DC voltage protection is there occurs malfunction, therefore simulation results show AC fault can cause DC voltage protection to miss It is dynamic.
Step 3-3：Increase exchanges the locking criterion that voltage is protected as DC voltage, i.e., increase by one in simulation model CL Compare Logic, when actual alternating voltage is less than alternating voltage setting valve, by DC voltage protection blocking, the protection mould after improvement Type is as shown in figure 8, simulation result shows that this corrective measure effectively avoids DC Line Fault and causes alternating voltage false protection Situation, demonstrating the improved method has feasibility.
The transient response feature of straight-flow system and flexible DC power transmission engineering direct current place are mainly matched somebody with somebody after combination failure occurs The protection put it could be assumed that, when three phase short circuit fault occurs：
（1）As shown in figure 9, when converting plant is constant DC voltage control, when three phase short circuit fault, converting plant input occur for converting plant Power drop, cause the unbalance of input power and power output, cause submodule capacitor voltage and DC voltage to drop, easily Cause DC low-voltage false protection；
（2）When Inverter Station as shown in Figure 10 is constant DC voltage control, when three phase short circuit fault, Inverter Station output occur for Inverter Station Power drop, cause the unbalance of input power and power output, cause submodule capacitor voltage and DC voltage to rise, easily Cause DC over-voltage protection malfunction.
DC Line Fault and the otherness of AC fault transient response feature are analyzed, proposes the corrective measure of direct current protecting.
Step 4-1：Step 4-1：Related criteria is obtained based on the equivalent circuit derivation of equation to divide DC Line Fault characteristic Analysis,
It is determined that alternating voltage u during direct current disconnection fault occursac1, find uac1Change unobvious.
Step 4-2：It is determined that alternating voltage u during three-phase alternating current failure occursac2, find uac2It is decreased obviously.
Step 4-3：Voltage of increasing exchanges is new locking criterion, when DC voltage exception, detects triple line electricity first It is pressed with valid value UacWhether setting valve U is dropped toac_setIf dropping to setting valve, the protection of locking DC voltage.Guarantor after improvement It is as shown in Figure 8 to protect model.

Claims (3)

  1. A kind of 1. improved method of MMC DC voltages protection, it is characterised in that：Its step is：
    Step 1：The locking criterion for determining DC voltage protection by carrying out qualitative analysis to MMC-HVDC system mathematic models：
    Step 1-1：MMC ac circuit equivalent equations can be obtained according to Kirchhoff's law：
    <mrow> <msub> <mi>u</mi> <mi>j</mi> </msub> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>L</mi> <mn>0</mn> </msub> <mfrac> <mrow> <msub> <mi>di</mi> <mi>j</mi> </msub> </mrow> <mrow> <mi>d</mi> <mi>t</mi> </mrow> </mfrac> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>R</mi> <mn>0</mn> </msub> <msub> <mi>i</mi> <mi>j</mi> </msub> <mo>+</mo> <mfrac> <mrow> <msub> <mi>u</mi> <mrow> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>u</mi> <mrow> <mi>p</mi> <mi>j</mi> </mrow> </msub> </mrow> <mn>2</mn> </mfrac> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>u</mi> <mrow> <mi>d</mi> <mi>c</mi> </mrow> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow>
    In formula (1)：Wherein ujFor alternating voltage, ijFor alternating current, upj、unjThe respectively upper and lower bridge arm voltage of j phases, udcTo be straight Flow voltage, L0For bridge arm inductance, R0For arm resistance, j=a, b, c,It is to alternating current ijDifferential；
    Step 1-2：DC voltage u is derived according to formula (1)dcEquivalent equation formula：
    <mrow> <msub> <mi>u</mi> <mrow> <mi>d</mi> <mi>c</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>u</mi> <mrow> <mi>p</mi> <mi>j</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>u</mi> <mrow> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>L</mi> <mn>0</mn> </msub> <mfrac> <mrow> <mi>d</mi> <mrow> <mo>(</mo> <msub> <mi>i</mi> <mrow> <mi>p</mi> <mi>j</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>i</mi> <mrow> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <mi>d</mi> <mi>i</mi> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow>
    Step 1-3：Analyzed according to circuit theory, obtain the total capacitance voltage equation of upper and lower bridge arm input：
    <mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msub> <mi>u</mi> <mrow> <mi>p</mi> <mi>j</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <msub> <mi>u</mi> <mi>j</mi> </msub> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>u</mi> <mrow> <mi>d</mi> <mi>c</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>u</mi> <mrow> <mi>d</mi> <mi>i</mi> <mi>f</mi> <mi>f</mi> <mi>j</mi> </mrow> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>u</mi> <mrow> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>u</mi> <mi>j</mi> </msub> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>u</mi> <mrow> <mi>d</mi> <mi>c</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>u</mi> <mrow> <mi>d</mi> <mi>i</mi> <mi>f</mi> <mi>f</mi> <mi>j</mi> </mrow> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow>
    Wherein ujFor alternating voltage, udiffjFor unbalance voltage drop inside jth phase；
    Step 1-4：According to above-mentioned formula (2), derive that MMC-HVDC occurs to cause DC voltage u during AC failuredcDecline While three-phase alternating voltage virtual value also reduce, but DC Line Fault will not cause alternating voltage virtual value to reduce, therefore carry Go out the locking criterion for protecting alternating voltage as DC voltage, when alternating voltage is less than setting valve DC voltage protection blocking；
    Step 2：Determine alternating voltage setting valve U in DC voltage protectionac_set, improve DC voltage protection：
    Step 2-1：Calculate and compare MMC-HVDC and occur to include single-phase grounding fault, two-phase short-circuit fault, two phase ground Alternating voltage virtual value during AC fault including short trouble, three phase short circuit fault, choose wherein maximum Uacmax1；
    Step 2-2：Alternating voltage is unaffected when MMC-HVDC generation DC sides break down, and is AC system output voltage Uac2；
    Step 2-3：Choose alternating voltage setting valve Uac_set, wherein
    <mrow> <msub> <mi>U</mi> <mrow> <mi>a</mi> <mi>c</mi> <mo>_</mo> <mi>s</mi> <mi>e</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>U</mi> <mrow> <mi>a</mi> <mi>c</mi> <mn>2</mn> </mrow> </msub> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>a</mi> <mi>c</mi> <mi>max</mi> <mn>1</mn> </mrow> </msub> </mrow> <mn>2</mn> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> <mo>;</mo> </mrow>
    Step 2-4：Alternating voltage setting valve U is introduced in the protection of MMC-HVDC DC voltagesac_set, measurement alternating voltage Uac, when Uac＜ Uac_setWhen DC voltage protection blocking, solve the problems, such as that AC fault easily causes DC voltage false protection.
  2. 2. the improved method of the MMC DC voltages protection according to claims 1, it is characterised in that：In PSCAD/EMTDC MMC-HVDC simulation models, verification method are built in emulation platform:
    Step 3-1：Mathematical modeling is built, builds the MMC-HVDC both-ends system of 11 level in PSCAD/EMTDC on this basis System simulation model, and commonly use protection for the soft straight engineering such as the protection of system configuration DC voltage, alternating voltage protection；
    Step 3-2：MMC-HVDC double ended systems simulation model include single-phase grounding fault, two-phase short-circuit fault, AC fault emulation including two-phase short circuit and ground fault, three phase short circuit fault, trouble point is arranged on transformer primary side, failure After generation DC voltage protection is there occurs malfunction, therefore simulation results show AC fault can cause DC voltage protection to miss It is dynamic；
    Step 3-3：Increase exchanges the locking criterion that voltage is protected as DC voltage, i.e., increase a comparison in simulation model Logic, when actual alternating voltage is less than alternating voltage setting valve, by DC voltage protection blocking, simulation result shows that this is changed Enter measure and effectively avoid the situation that DC Line Fault causes alternating voltage false protection, demonstrate the improved method have it is feasible Property.
  3. 3. the improved method of the MMC DC voltages protection according to claims 1, it is characterised in that：It is single-phase in step 2-1 During earth fault：Alternating voltage virtual value is calculated, using A phases as failure phase, i.e. UA=0, non-faulting phase voltage formula is calculated as follows：
    <mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msub> <mi>U</mi> <mi>B</mi> </msub> <mo>=</mo> <msub> <mi>U</mi> <mn>0</mn> </msub> <mo>+</mo> <msup> <mi>a</mi> <mn>2</mn> </msup> <msub> <mi>U</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>aU</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mo>(</mo> <msup> <mi>a</mi> <mn>2</mn> </msup> <mo>-</mo> <mn>1</mn> <mo>)</mo> <msub> <mi>Z</mi> <mn>0</mn> </msub> <mo>+</mo> <mo>(</mo> <msup> <mi>a</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>a</mi> <mo>)</mo> <msub> <mi>Z</mi> <mn>2</mn> </msub> </mrow> <mrow> <msub> <mi>Z</mi> <mn>0</mn> </msub> <mo>+</mo> <msub> <mi>Z</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>Z</mi> <mn>2</mn> </msub> </mrow> </mfrac> <msub> <mi>E</mi> <mi>A</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>U</mi> <mi>C</mi> </msub> <mo>=</mo> <msub> <mi>U</mi> <mn>0</mn> </msub> <mo>+</mo> <msub> <mi>aU</mi> <mn>1</mn> </msub> <mo>+</mo> <msup> <mi>a</mi> <mn>2</mn> </msup> <msub> <mi>U</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mo>(</mo> <mi>a</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> <msub> <mi>Z</mi> <mn>0</mn> </msub> <mo>+</mo> <mo>(</mo> <msup> <mi>a</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>a</mi> <mo>)</mo> <msub> <mi>Z</mi> <mn>2</mn> </msub> </mrow> <mrow> <msub> <mi>Z</mi> <mn>0</mn> </msub> <mo>+</mo> <msub> <mi>Z</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>Z</mi> <mn>2</mn> </msub> </mrow> </mfrac> <msub> <mi>E</mi> <mi>A</mi> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow>
    E in formulaAIt is failure phase-to-ground voltage, Z0、Z1、Z2It is the zero sequence, positive sequence, negative sequence impedance entered from the point of view of failure,Complex factor, that is, when singlephase earth fault occurs, Uacmax1=UB=UC。
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CN113241741A (en) * 2021-05-14 2021-08-10 广东电网有限责任公司电力调度控制中心 Direct-current line protection method, device and equipment for preventing false start of alternating-current fault

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CN103063903A (en) * 2012-12-10 2013-04-24 国网智能电网研究院 Overvoltage computing method of modular multi-level converter
CN104393572A (en) * 2014-11-17 2015-03-04 南京南瑞继保电气有限公司 Method and system for configuring overvoltage protection of modular multilevel converter
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CN103063903A (en) * 2012-12-10 2013-04-24 国网智能电网研究院 Overvoltage computing method of modular multi-level converter
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