CN107069679A - A kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods - Google Patents
A kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods Download PDFInfo
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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
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Abstract
The present invention proposes a kind of symmetrical bipolar MMC DC sides monopolar grounding fault and passed through and restoration methods.The present invention by the cooperation of dc circuit breaker and transverter, realize to direct fault current cut-off and power recovery, protect the safe operation of transverter.Coordinate the active power shortage of current conversion station during reducing failure by perfecting the active power and reactive power of pole and failure pole, while providing specified reactive power to power network, reduce impact of the failure to AC system；Pass through the active control to the upper and lower bridge arm reference voltage common mode component of transverter, it is to avoid the risk that transverter current surge stress excessive caused by unsuccessful reclosing is brought to system safety operation.Both positive and negative polarity dc bus can be regarded as based on the bipolar short trouble of symmetrical bipolar MMC DC sides generation a kind of special circumstances of monopolar grounding fault occur respectively, therefore the present invention can be additionally used in symmetrical bipolar MMC DC sides and occur the processing of bipolar short trouble.
Description
Technical field
The invention belongs to flexible high pressure DC transmission system DC error protection field, more particularly, to a kind of symmetrical
Bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods.
Background technology
The problems such as due to energy shortage and environmental protection, increasingly highlights, and the novel renewable energy such as wind-force and solar energy generates electricity
The ratio that amount accounts for gross generation gradually increases.In China, wind energy, solar energy equal energy source have focused largely on remote districts, caused
The location distribution of the energy and load is unbalanced, it is necessary to long range, Large Copacity conveying electric energy.Applied to long range, great Rong
During amount transmission of electricity, the cost and reactive loss of high-voltage AC transmission system increase sharply with the increase of transmission distance.Therefore, high pressure
HVDC Transmission Technology gradually causes the concern of domestic and foreign scholars, and has obtained rapid development.
D.C. high voltage transmission HVDC based on voltage source type converter VSC (Voltage Source Converter)
(High-Voltage Direct-Current) technology has relative to Traditional DC technology of transmission of electricity：Without reactive-load compensation, do not have
Commutation failure risk, can be caused domestic and foreign scholars and is widely closed with advantages such as the active and reactive powers of separately adjustable system
Note.Compared to traditional two level and three-level topology structure, modularization multi-level converter MMC (Modular
Multilevel Converter) there is structure height modularization, be easy to extension, without multi-winding isolation transformer and output electricity
The low advantage of harmonic wave is pressed, is applied in Practical Project, the end of Zhoushan five of such as the Transbay engineerings in the U.S., China is flexible
DC transmission engineering.
Symmetrical bipolar connection plan is one of main Main Wire Connection Scheme of current MMC-HVDC systems.Symmetrical bipolar MMC phases
Have the advantages that the method for operation is flexible, transmission capacity is big, reliability is high, bipolar individually controllable than symmetrical monopolar MMC.It is symmetrical bipolar
MMC is in DC side both positive and negative polarity neutral earthing, and both positive and negative polarity is relatively independent.When a pole of system hinders out of service for some reason, Ling Yiji
Normal operation is remained to, and keeps the specified transmission capacity of half.The current symmetrical bipolar DC transmission engineering put into operation has Xiamen
Flexible DC power transmission engineering.
However, the protection of symmetrical bipolar MMC direct currents side pole fault to ground is still the significant challenge in Practical Project.It is existing
MMC-HVDC systems in it is many using devices are few, cost economic half-bridge submodule HBSM (Half-Bridge SM).Due to
HBSM does not have DC Line Fault self-cleaning ability, then system can produce excessive fault current.This not only can be to the device of transverter
Part is caused damage, and larger impact can be also produced to AC system, the stability of AC system is influenceed.In the prior art, handle
Symmetrical bipolar MMC DC sides monopolar grounding fault mainly has following several method：
1) using the submodule with DC Line Fault Scavenging activity.After monopolar grounding fault occurs for DC side, submodule
Locking immediately.Setting up backward voltage by submodule electric capacity forces fault current to be decayed rapidly.But the submodule that this method is used
Block needs extra switching device to cause construction cost higher compared to half-bridge MMC, and running wastage is larger.During failure, the change of current
Device locking is big to the power rush of AC system.
2) high voltage DC breaker is used.When monopolar grounding fault occurs for DC side, dc circuit breaker, which is performed, cut-offs behaviour
Make to cut-off direct fault current.In this way during failure, because failure is extremely out of service, cause what system was transmitted
Rated active power have lost half so that active power shortage is big.Meanwhile, when dc circuit breaker attempts reclosing, if weight
Close a floodgate and fail, then failure pole is equivalent to occurring " second short circuit ", and huge surge current stress will endanger transverter safe operation.
In summary, when handling symmetrical bipolar MMC generations monopolar grounding fault using HVDC short-circuiting device, exist active
Power shortage is big, the problem of surge current stress is big during reclosing.
The content of the invention
For the disadvantages described above or Improvement requirement of prior art, the invention provides the event over the ground of symmetrical bipolar MMC direct currents pole
The traversing method and recovery policy of barrier, it is intended to solve prior art active power shortage during direct current side pole fault to ground it is big with
And during dc circuit breaker reclosing the problem of surge current stress is big.
To achieve the above object, the present invention proposes that a kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and recovered
Method.The DC transmission system that the present invention is applicable is included comprising two connection transformers, two MMC and two dc bus,
Symmetrical bipolar MMC is in DC side both positive and negative polarity neutral earthing.The MMC includes A, B, C three-phase, and upper and lower two bridge arms are included per phase,
Each bridge arm is made up of n half-bridge sub-module cascade, one bridge arm inductance of concatenation.The half-bridge submodule is by two IGBT and two
Individual antiparallel diode, one electric capacity of connection is constituted, and the half-bridge submodule, which also includes one, is used for the brilliant lock of error protection
Pipe.Every described dc bus concatenates a smoothing reactor and a dc circuit breaker；It is assumed that being sent out in described positive pole
Raw monopolar grounding fault, then claim just extremely failure pole, and negative pole is perfects pole.It is characterised in that it includes following steps：
(1) differentiate whether MMC DC sides occur monopolar grounding fault；
It is then to perform following act：Failure pole MMC block signals are sent, are made in all half-bridge submodules of failure pole MMC
IGBT is all off, to block the discharge path of the half-bridge submodule electric capacity；The bypass IGCT for sending half-bridge submodule is led
Messenger, bypasses antiparallel diode in the half-bridge submodule, to protect anti-paralleled diode；The direct current of failure pole is broken
Road device sends open command, blocks the short circuit path of AC network；
Otherwise system keeps stable state control model；
The MMC refers to modularization multi-level converter；
(2) after bus direct fault current decays to zero, failure pole MMC unlocking signals is sent, failure pole is transferred to
STATCOM operational modes, reactive power support is persistently provided to AC；
(3) when dc bus goes free process to terminate, that is, when recovering dielectric level, to the dc circuit breaker on dc bus
Send reclosing signal；
(4) whether the surge current stress of Judging fault pole dc bus is excessive；
It is to show that temporary fault is not eliminated, is sent to the dc circuit breaker and back off signal, isolated fault
Point；Go to step (5)；
Otherwise show that temporary fault has been eliminated, send progressively recovery power transmission signal to failure pole MMC, make its turn
Enter stable state control model；Turn to terminate；
(5) judge whether the dc circuit breaker is more than presetting excessively stream number of times by the number of times of electric current overrate；
It is MMC is kept STATCOM operational modes, direct-current short circuit device no longer carries out reclosing trial, turns to terminate；Otherwise go to step
(1)；Presetting excessively stream number of times takes 2~3 times.
The traversing method and recovery policy for the symmetrical MMC monopolar grounding faults that the present invention is provided are by transverter and direct current
What breaker cooperation was realized.During failure, locking transverter cut-offs dc circuit breaker to protect the peace of failure pole transverter
Row for the national games.In the case where considering the limitation of multi-constraint condition, coordinate to match somebody with somebody by perfecting the active power and reactive power of pole and failure pole
Close, overload is run on when making to perfect extremely short, reduce power shortage of the system during failure.Meanwhile, run failure pole
In STATCOM states persistently to provide reactive power support to AC and reduce impact to AC system.By to MMC transverters
The active control of upper and lower bridge arm reference voltage common mode component, can effectively be reduced because of the wave that dc circuit breaker unsuccessful reclosing is produced
Gush current-rising-rate.
Preferably, the step (2) includes following sub-step：
(2-1) is pressed according to converter power transformer capacity, MMC bridge arms through-current capability, half-bridge submodule, submodule capacitor voltage
Fluctuation and DC line overload capacity constraints, try to achieve the active power for perfecting pole MMC and reactive power operation region；
In the active power and reactive power operation region, adjustment perfects pole MMC stable operations operating point, it is run on mistake in short-term
Carry, with transmitting active power as much as possible, so as to make up the power shortage of monopolar grounding fault；
(2-2) transmits twice of rated reactive power signal during being emitted in failure to the failure pole MMC, make described strong
The rated reactive power of full pole MMC required transmission in the steady state is undertaken by failure pole MMC.
Preferably, the restrictive condition of converter power transformer capacity is described in the step (2-1)：
The transmission capacity S of active-power P, reactive power Q and converter power transformer that transverter is transmittedmaxMeet：
P2+Q2＜ Smax 2；
Wherein, active-power P, reactive power Q are respectively the active and reactive power that MMC is flowed to from PCC, SmaxFor the change of current
The maximum transfer capacity of transformer.
Preferably, the restrictive condition of MMC bridge arm through-current capabilities is described in the step (2-1)：
Each bridge arm current is met：
Wherein, IlimFor the maximum current capacity of each IGBT in submodule, UdcFor single MMC DC bus-bar voltage, Usm
For ac bus voltage magnitude；Rectification direction is positive direction.
Preferably, the restrictive condition that each half-bridge submodule is pressed in the step (2-1) is：
The DC component of each bridge arm current is necessarily less than AC compounent；I.e. active-power P and reactive power Q are met：
Preferably, the restrictive condition of voltage fluctuation of capacitor is in each submodule：
During MMC steady-state operations, voltage fluctuation of capacitor no more than the permitted maximum range of submodule, i.e.,：
Wherein, N is submodule quantity, and C is submodule capacitance, UcFor submodule rated voltage, k modulates for built-in potential
Than submodule capacitor voltage fluctuation percentageIts maximum is εmax.Transverter institute
The reactive power Q of transmissioncBy the difference of Q and AC equivalent inductance the L reactive power consumedI.e.XLFor the induction reactance X of AC equivalent inductanceL=ω L, ω are angular frequency.
Preferably, DC line overload capacity described in the step (2-1) is met：
The short-time overload capacity limit of DC current no more than DC line, i.e.,
Wherein, idcFor DC bus current, idc_maxFor the DC line short-time overload capacity limit.
Preferably, after the step (2-1), step (2-2), following steps are also performed：
(2-3) is superimposed auxiliary voltage on the upper and lower bridge arm reference voltages of MMCMake the upper and lower bridges of MMC
Arm voltage is：The superposition auxiliary voltage reduces the rising of surge current
Rate, the risk brought with the current surge stress for avoiding transverter excessive caused by unsuccessful reclosing to system safety operation；
Wherein, δ is PCC point built-in potentials evRelative to ac bus voltage usPhase difference, idcFor failure dc bus electricity
Stream (rectification direction is positive direction),For DC current reference value, R (R>0) it is damped coefficient, up_upFor bridge arm voltage on MMC,
up_downFor bridge arm voltage under MMC；If dc circuit breaker reclosing success, due to the presence of the flat ripple reactance of direct current, idcIt will not go out
Existing surge current, therefore cut-off stream current reference valueIf dc circuit breaker unsuccessful reclosing, surge current idcOn rapid
Rise.
In the present invention, when dc circuit breaker unsuccessful reclosing, (i.e. active resistance can be suppressed by the active control of transverter
Buddhist nun control) system produce huge surge current stress.
In general, by the contemplated above technical scheme of the present invention compared with prior art, with following beneficial effect
Really：
Direct fault current is cut-off 1. being realized by the cooperation of dc circuit breaker and transverter, protection transverter
Safe operation.After Failure elimination, the foundation of DC voltage and the recovery of power are realized.
2. during failure, make to perfect pole meeting converter power transformer capacity, bridge arm through-current capability, half-bridge submodule and press need
Ask, submodule capacitor voltage fluctuation and the several aspects of DC line overload capacity constraints under, run on short-time overload shape
State, with transmitting active power as much as possible, so that the power shortage of monopolar grounding fault is made up, while changing the transmission of failure pole
Flow whole rated reactive powers needed for station.Event is reduced by active power and the reactive power cooperation for perfecting pole and failure pole
The active power shortage of current conversion station during barrier, while providing specified reactive power to power network, reduces failure to AC system
Impact.
3. during failure, by the active control to the upper and lower bridge arm reference voltage common mode components of MMC, effectively reduce
The climbing of surge current, it is to avoid transverter current surge stress excessive caused by unsuccessful reclosing gives system safety
Run the risk brought.
4. due to based on symmetrical bipolar MMC in DC side both positive and negative polarity neutral earthing, DC side occur it is bipolar it is short-circuit can
Regard both positive and negative polarity dc bus as and a kind of special circumstances of monopolar grounding fault occur respectively.Therefore, base proposed by the invention
Passed through in symmetrical bipolar MMC DC side monopolar grounding fault and recovery policy is equally applicable to symmetrical bipolar MMC DC sides
The bipolar short trouble of generation.
Brief description of the drawings
Fig. 1 is the symmetrical bipolar MMC flexible direct-current system topology schematic of both-end；
Fig. 2 is symmetrical bipolar half-bridge MMC topological structure and monopolar grounding fault schematic diagram；
Fig. 3 DC side monopolar grounding faults are passed through and recovery policy flow chart；
Fig. 4 is surge current stress optimization control block diagram；
Active-power P and reactive power Q can range of operation schematic diagrames during Fig. 5 is failure；
Wherein, Fig. 5 (a) considers converter power transformer capacity and the active power and reactive power of the limitation of bridge arm through-current capability
Can range of operation schematic diagram；Fig. 5 (b) considers the active power for the limitation that converter power transformer capacity is fluctuated with submodule capacitor voltage
Can range of operation schematic diagram with reactive power；Fig. 5 (c) considers converter power transformer capacity and the limitation of DC line overload capacity
Active power and reactive power can range of operation schematic diagrames；
Fig. 6 is to perfect pole and failure pole active reactive Power operation scope schematic diagram during failure under many limiting factors；
Fig. 7 is that the symmetrical bipolar semi-bridge type MMC DC Line Faults for being not introduced into the control of surge current stress optimization pass through emulation knot
Really；Wherein, Fig. 7 (A) representing faults pole, Fig. 7 (B), which is represented, perfects pole.
Wherein, Fig. 7 (A1) be failure pole DC bus-bar voltage (kV), Fig. 7 (A2) be failure pole DC bus current (kA),
Fig. 7 (A3) is that active and reactive power (MW/MVar), Fig. 7 (A4) of the PCC points transmission of failure pole are failure pole ac-side currents
(kA), Fig. 7 (A5) is that failure pole upper and lower bridge arm submodule capacitor voltage (kV), Fig. 7 (A6) are the bridge arm currents of failure pole six
(kA)；Fig. 7 (B1) is that to perfect pole DC bus-bar voltage (kV), Fig. 7 (B2) be to perfect pole DC bus current (kA), Fig. 7 (B3)
It is that to perfect the active of pole PCC points transmission with reactive power (MW/MVar), Fig. 7 (B4) be to perfect pole ac-side current (kA), Fig. 7
(B5) it is that to perfect pole upper and lower bridge arm submodule capacitor voltage (kV), Fig. 7 (B6) be to perfect the bridge arm current (kA) of pole six；
Fig. 8 is that the symmetrical bipolar semi-bridge type MMC DC Line Faults for introducing surge current stress optimization control strategy pass through emulation
As a result.
Embodiment
In order to make the purpose , technical scheme and advantage of the present invention be clearer, it is right below in conjunction with drawings and Examples
The present invention is further elaborated.It should be appreciated that specific embodiment described herein is only to explain the present invention, not
For limiting the present invention.As long as in addition, technical characteristic involved in each embodiment of invention described below that
Not constituting conflict between this can just be mutually combined.
The present invention describes symmetrical bipolar MMC monopolar grounding faults by taking the symmetrical bipolar MMC of both-end as an example and passed through and recovery policy.
Fig. 1 is the symmetrical bipolar MMC system topology schematics of both-end, includes two current conversion stations.Each current conversion station is using symmetrical bipolar master
The mode of connection, as shown in Figure 2.Symmetrical bipolar MMC includes two connection transformers, two in DC side both positive and negative polarity neutral earthing
MMC and two dc bus.Every dc bus concatenates a smoothing reactor and a dc circuit breaker；Each MMC bags
Containing A, B, C three-phase, per upper and lower two bridge arms are mutually included, each bridge arm concatenates a bridge arm electricity by N number of half-bridge sub-module cascade
Sense is constituted.Semi-bridge type MMC topological structure schematic diagram, as shown in Figure 3.Half-bridge submodule is antiparallel by two IGBT and two
Diode, one electric capacity of connection are constituted, and described half-bridge submodule, which also includes one, is used for the IGCT of error protection.It is assumed that
Monopolar grounding fault occurs for described positive pole, then claims just extremely failure pole, and negative pole is perfects pole.
Fault traversing of the present invention and recovery policy are related to cooperation such as Fig. 4 institutes of transverter and dc circuit breaker
Show, specifically include following steps：
(1) differentiate whether MMC DC sides occur monopolar grounding fault, be then to perform following act：Failure pole MMC is sent to close
Lock signal, makes IGBT in all half-bridge submodules of failure pole MMC all off, to block the electric discharge of the half-bridge submodule electric capacity
Path；The bypass turn on thyristors signal of half-bridge submodule is sent, antiparallel diode in the half-bridge submodule is bypassed, with
Protect anti-paralleled diode；Open command is sent to the dc circuit breaker of failure pole, the short circuit path of AC network is blocked；Otherwise
System keeps stable state control model；The MMC refers to modularization multi-level converter；
(2) after bus direct fault current decays to zero, failure pole MMC unlocking signals is sent, failure pole is transferred to
STATCOM operational modes, reactive power support is persistently provided to AC；
(3) when dc bus goes free process to terminate and (recover dielectric level), to the direct current interruption on dc bus
Device sends reclosing signal；
(4) whether the surge current stress of Judging fault pole dc bus is excessive；It is to show that temporary fault is not clear
Remove, sent to the dc circuit breaker and back off signal, isolated fault point；Go to step (5)；Otherwise temporary fault is shown
It is eliminated, sends progressively recovery power transmission signal to failure pole MMC, it is transferred to stable state control model；Turn to terminate；
(5) judge whether the dc circuit breaker is more than presetting excessively stream number of times by the number of times of electric current overrate；
It is MMC is kept STATCOM operational modes, direct-current short circuit device no longer carries out reclosing trial, turns to terminate；Otherwise go to step
(1)；Presetting excessively stream number of times takes 2~3 times.
As a kind of prioritization scheme, the step (2) includes following sub-step：
(2-1) is pressed according to converter power transformer capacity, MMC bridge arms through-current capability, half-bridge submodule, submodule capacitor voltage
Fluctuation and DC line overload capacity constraints, try to achieve the active power for perfecting pole MMC and reactive power operation region；
In the active power and reactive power operation region, adjustment perfects pole MMC stable operations operating point, it is run on mistake in short-term
Carry, with transmitting active power as much as possible, so as to make up the power notch of monopolar grounding fault；
(2-2) transmits twice of rated reactive power signal during being emitted in failure to the failure pole MMC, make described strong
The rated reactive power of full pole MMC required transmission in the steady state is undertaken by failure pole MMC.
As a kind of prioritization scheme, the restrictive condition of converter power transformer capacity is described in the step (2-1)：
The transmission capacity S of active-power P, reactive power Q and converter power transformer that transverter is transmittedmaxMeet：
P2+Q2＜ Smax 2；
Wherein, active-power P, reactive power Q are respectively from points of common connection PCC (Point of Common
Coupling MMC active and reactive power, S) are flowed tomaxFor the maximum transfer capacity of converter power transformer.
As a kind of prioritization scheme, the restrictive condition of MMC bridge arm through-current capabilities is described in the step (2-1)：
Each bridge arm current is met：
Wherein, IlimFor the maximum current capacity of each IGBT in submodule, UdcFor single MMC DC bus-bar voltage, Usm
For ac bus voltage magnitude；Rectification direction is positive direction.(// note：Here power represents direction, and rectification direction is retouched for positive direction
It is more accurate to state, so write it will be realized that.//)
As a kind of prioritization scheme, the restrictive condition that each half-bridge submodule is pressed in the step (2-1) is：
The DC component of each bridge arm current is necessarily less than AC compounent；I.e. active-power P and reactive power Q are met：
As a kind of prioritization scheme, the restrictive condition of voltage fluctuation of capacitor is in each submodule：
During MMC steady-state operations, capacitance voltage ripple rate no more than the permitted maximum range of submodule, i.e.,：
Wherein, N is submodule quantity, and C is submodule capacitance, UcFor submodule rated voltage, k modulates for built-in potential
Than submodule capacitor voltage fluctuation percentageIts maximum is εmax.Transverter institute
The reactive power Q of transmissioncBy the difference of Q and AC equivalent inductance the L reactive power consumedI.e.XLFor the induction reactance X of AC equivalent inductanceL=ω L, ω are angular frequency.
As a kind of prioritization scheme, DC line overload capacity described in the step (2-1) is met：
The short-time overload capacity limit of DC current no more than DC line, i.e.,
Wherein, idcFor DC bus current, idc_maxFor the DC line short-time overload capacity limit.
As a kind of prioritization scheme, after the step (2-1), step (2-2), following steps are also performed：
(2-3) is superimposed auxiliary voltage on the upper and lower bridge arm reference voltages of MMCMake the upper and lower bridges of MMC
Arm voltage is：The superposition auxiliary voltage reduces the rising of surge current
Rate, the risk brought with the current surge stress for avoiding transverter excessive caused by unsuccessful reclosing to system safety operation；
Wherein, δ is PCC point built-in potentials evRelative to ac bus voltage usPhase difference, idcFor failure dc bus electricity
Stream (rectification direction is positive direction),For DC current reference value, R (R>0) it is damped coefficient, up_upFor bridge arm voltage on MMC,
up_downFor bridge arm voltage under MMC；If dc circuit breaker reclosing success, due to the presence of the flat ripple reactance of direct current, idcIt will not go out
Existing surge current, therefore cut-off stream current reference valueIf dc circuit breaker unsuccessful reclosing, surge current idcOn rapid
Rise.
The traversing method and recovery policy for the symmetrical bipolar MMC monopolar grounding faults that the present invention is provided are by MMC and straight
Flow what breaker cooperation was realized.During failure, MMC lockings cut-off dc circuit breaker to protect the peace of failure pole transverter
Row for the national games.In the case where considering the limitation of multi-constraint condition, coordinate to match somebody with somebody by perfecting the active power and reactive power of pole and failure pole
Close, overload is run on when making to perfect extremely short, reduce power shortage of the system during failure.Meanwhile, run failure pole
In STATCOM states persistently to provide reactive power support to AC and reduce impact to AC system.By to MMC transverters
The active control of upper and lower bridge arm reference voltage common mode component, the surge that effectively reduction is produced by dc circuit breaker unsuccessful reclosing
Current-rising-rate.
To make those skilled in the art more fully understand the present invention, with reference to symmetric double of the specific embodiment to the present invention
Pole semi-bridge type MMC monopolar grounding faults are passed through to be described in detail with recovery policy.
This example uses the data of Zhangbei County's flexible DC power transmission engineering, and sub-modular structure uses the knot of semi-bridge type submodule
Structure, systematic parameter is：Dc bus rated voltage is 500kV, and rated power is 1500MW, and bridge arm inductance is 80mH, Mei Geqiao
Arm includes 218 submodule numbers, and submodule electric capacity is 15mF, and submodule rated voltage is 2.294kV.Transformer uses Y0/ △
Bind mode, net side/valve side no-load voltage ratio (l-l, rms) is 525/260kV, and rated impedance perunit value is 15%, rated capacity
1700MVA.It is assumed that each pole transverter provides 450MVar reactive power, i.e., the stable state of each pole to AC during stable state
Acceptable operating point is P (1500MW, -450MVar).The present invention is so that failure occurs at positive direct-current bus as an example, such as Fig. 2.
Analyze MMC active power and reactive power operation regional extent：Converter power transformer capacity, bridge arm through-current capability, half
Bridge submodule is pressed, submodule capacitor voltage is fluctuated, DC line overload capacity is determined by following formula respectively：P2+Q2＜
Smax 2、
The symmetrical bipolar MMC DC power transmission lines of both-end are used as using overhead line.After monopolar grounding fault is detected, failure
Pole MMC transverters are switched to fault traversing control model：The locking immediately of failure pole transverter, and turn on the bypass of half-bridge submodule
IGCT, while dc circuit breaker, which is immediately performed, cut-offs operation.After direct fault current decays to zero, failure pole transverter
Unblock, is transferred to STATCOM operational mode.
During failure, perfect pole short-time overload under conditions of many limiting factors are considered, failure pole transmission current conversion station
Whole rated reactive powers.Meanwhile, during failure, auxiliary voltage u is superimposed on upper and lower bridge arm reference voltagez,Upper and lower bridge arm voltage is：
When DC power transmission line goes free process to terminate, due to using open-wire transmission line, DC side monopolar grounding fault is more
For non-permanent failure, therefore this example has carried out voltage twice recovers to attempt.If there is huge surge current stress, direct current breaks
Road device is backed off, isolated fault point；If there is not huge surge current stress, failure pole MMC progressively recovers power biography
It is defeated, finally it is transferred to stable state control model.Meanwhile, judge whether DC bus current exceedes DC bus current rated value number of times big
In presetting excessively stream number of times, if so, then MMC keeps current state, direct-current short circuit device no longer carries out reclosing trial；Otherwise direct current
Breaker is backed off, and repeats above step.
Pressed by converter power transformer capacity, bridge arm through-current capability, half-bridge submodule, submodule capacitor voltage is fluctuated, direct current
The constraints of circuit overload ability can obtain the operation area of active power and reactive power, as shown in Figure 5.As a result show：MMC
Active power and reactive power can range of operation and bridge arm through-current capability, submodule capacitor voltage fluctuation maximum and AC line
Loading capability is passed by into positive correlation.The parameter for taking multiple limiting factors during failure is：MMC bridge arms are through-flow, and maximum current capacity is
1.1pu, the maximum allowable stability bandwidth of submodule capacitor voltage is 1.1pu, and DC line overload capacity is 1.2pu, then can obtain such as
Active power and reactive power shown in Fig. 6 can operation area scope (shadow region for can operation area), as a result show：Direct current
During failure, perfect pole and can run on operating point P2 (1700MW, 0MVar), failure pole can run on operating point P1 (0MW ,-
900MVar).MMC can provide 1700MW active power and 900MVar reactive power during failure.The fault traversing phase
Between, by perfecting the active power and the cooperation of reactive power of pole and failure pole, it can not only continue to provide to AC
Nominal reactive is supported, and can overcome the disadvantages that the power shortage of failure pole 11.76%.
Assuming that ground short circuit failure, the fault clearance after 450ms occur in 1s for positive direct-current bus.Fig. 7 is based on symmetrical
The semi-bridge type MMC simulation results of bipolar main electrical scheme, (A) represents failure pole, and (B) represents to perfect pole.Failure pole DC bus current
As shown in Fig. 7 (A2), as a result show：Dc circuit breaker is cut-off after DC Line Fault, and fault current decays to zero.Perfect pole and failure
The active power of pole is with shown in reactive power such as Fig. 7 (A3) and Fig. 7 (B3), as a result showing：Transverter can be carried during failure
The reactive power of active power and 900MVar for 1700MW.By perfecting pole and failure pole during demonstrating fault traversing
Active and reactive power, which coordinates, can continue to provide nominal reactive support to AC, and can overcome the disadvantages that failure pole 11.76%
The conclusion of power shortage.Perfect pole upper and lower bridge arm submodule capacitor voltage and six bridge arm currents such as Fig. 7 (B5) and Fig. 7 (B6) institute
Show, as a result show：When perfecting pole transverter and running on short-time overload state, submodule capacitor voltage fluctuation percentage is specified
1.11 times of value, MMC bridge arms maximum current is 1.104 times of rated value, is coincide substantially with theory analysis.Perfect pole and failure pole
Ac-side current such as Fig. 7 (A4) and Fig. 7 (B4) shown in, as a result show：Whole fault traversing and recovery control, smoothly, quickly,
Without impact.
After dc circuit breaker isolated DC failure, go to dissociate through the 300ms times, then carry out reclosing.Due to now, directly
Stream failure is not yet eliminated, therefore can produce huge surge current stress.As a result as shown in Fig. 7 (A).As a result show：If
System failure unsuccessful reclosing, if being added without surge current Optimal Control Strategy, voltage step and current surge current stress are big；
Meanwhile, power and the bridge arm voltage fluctuation of system are also very big, and the safe operation to system brings risk.
Introduce after surge current optimal control, for different damped coefficient R, the surge current stress of system is carried out
Contrast simulation.Simulation result is as shown in Figure 8.As a result show：With damped coefficient R increase, dc circuit breaker loses in reclosing
Surge current stress caused by after losing is gradually reduced, and this fully demonstrates the validity of proposed optimisation strategy.However, entering one
Step is it can be found that with damped coefficient R increase, the inhibition to surge current is gradually reduced.This is due to semi-bridge type MMC
Bridge arm voltage output area be：0≤uarm≤Udc.With damped coefficient R increase, auxiliary voltage uzGradually increase so that
The reference voltage of upper and lower bridge arm reaches the limit of fan-out capability, so that the inhibition to surge current is reduced.
Dc circuit breaker detects after surge current isolated DC failure again.Again pass by 300ms goes the free time
Afterwards, second of trial of dc circuit breaker carries out reclosing, and final system is successfully recovered.
As it will be easily appreciated by one skilled in the art that the foregoing is merely illustrative of the preferred embodiments of the present invention, it is not used to
The limitation present invention, any modifications, equivalent substitutions and improvements made within the spirit and principles of the invention etc., it all should include
Within protection scope of the present invention.
Claims (8)
1. a kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods, it is characterised in that including following step
Suddenly：
(1) differentiate whether MMC DC sides occur monopolar grounding fault：
It is then to perform following act：Failure pole MMC block signals are sent, make IGBT in all half-bridge submodules of failure pole MMC complete
Portion is turned off, to block the discharge path of the half-bridge submodule electric capacity；The bypass turn on thyristors signal of half-bridge submodule is sent,
Antiparallel diode in the half-bridge submodule is bypassed, to protect anti-paralleled diode；To the dc circuit breaker hair of failure pole
Go out open command, block the short circuit path of AC network；Act above in no particular order；The MMC refers to the modular multilevel change of current
One pole of DC side earth fault extremely occurs for device, the failure；Go to step (2)；
Otherwise system keeps stable state control model, goes to step (6)；
(2) after bus direct fault current decays to zero, failure pole MMC unlocking signals are sent, failure pole MMC is transferred to nothing
Work(compensates STATCOM (Static Synchronous Compensator) operational mode, and idle branch is persistently provided to AC
Support；
(3) when failure pole dc bus goes free process to terminate, that is, when recovering dielectric level, to the direct current interruption on dc bus
Device sends reclosing signal；
(4) whether the surge current stress on the dc bus of Judging fault pole is excessive；
It is to show that failure is not eliminated, is sent to the dc circuit breaker on the dc bus of the failure pole and back off signal,
Isolated fault point；Go to step (5)；
Otherwise show that temporary fault has been eliminated, send progressively recovery power transmission signal to failure pole MMC, it is transferred to surely
State control model, goes to step (6)；
(5) judge whether the dc circuit breaker is more than default excessively stream number of times by the number of times of electric current overrate；It is to make
MMC keeps STATCOM operational modes, and direct-current short circuit device no longer carries out reclosing trial, gone to step (6)；Otherwise go to step (1)；
The presetting excessively stream number of times takes 2~3 times；
(6) terminate.
2. fault traversing according to claim 1 and restoration methods, it is characterised in that the step (2) includes following son
Step：
(2-1) is pressed according to converter power transformer capacity, MMC bridge arms through-current capability, half-bridge submodule, submodule capacitor voltage fluctuation
With DC line overload capacity constraints, the active power for perfecting pole MMC and reactive power operation region are determined；At this
In active power and reactive power operation region, adjustment perfects pole MMC stable operations operating point, it is run on short-time overload,
With transmitting active power as much as possible, so as to make up power shortage caused by monopolar grounding fault；
Twice of rated reactive power signal of transmission during (2-2) is emitted in failure to the failure pole MMC, makes described to perfect pole
The rated reactive power of MMC required transmission in the steady state is undertaken by failure pole MMC.
3. fault traversing according to claim 2 and restoration methods, it is characterised in that changed described in the step (2-1)
The restrictive condition of convertor transformer capacity is：
The transmission capacity S of active-power P, reactive power Q and converter power transformer that transverter is transmittedmaxMeet：P2+Q2＜
Smax 2；
Wherein, active-power P, reactive power Q are respectively from points of common connection PCC (Point of Common Coupling) streams
To MMC active and reactive power, SmaxFor the maximum transfer capacity of converter power transformer.
4. fault traversing according to claim 2 and restoration methods, it is characterised in that MMC described in the step (2-1)
The restrictive condition of bridge arm through-current capability is：
Each bridge arm current is met：
Wherein, IlimFor the maximum current capacity of each IGBT in submodule, UdcFor single MMC DC bus-bar voltage, UsmFor exchange
Busbar voltage amplitude；Rectification direction is positive direction.
5. fault traversing according to claim 2 and restoration methods, it is characterised in that each half-bridge in the step (2-1)
The restrictive condition that submodule is pressed is：
The DC component of each bridge arm current is necessarily less than AC compounent；I.e. active-power P and reactive power Q are met：
6. fault traversing according to claim 2 and restoration methods, it is characterised in that voltage fluctuation of capacitor in each submodule
Restrictive condition be：
During MMC steady-state operations, voltage fluctuation of capacitor no more than the permitted maximum range of submodule, i.e.,：
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Wherein, N is submodule quantity, and C is submodule capacitance, UcFor submodule rated voltage, k is built-in potential modulation ratio, submodule
Block voltage fluctuation of capacitor percentageIts maximum is εmax.What transverter was transmitted
Reactive power QcBy the difference of Q and AC equivalent inductance the L reactive power consumedI.e.XLFor the induction reactance X of AC equivalent inductanceL=ω L, ω are angular frequency.
7. fault traversing according to claim 2 and restoration methods, it is characterised in that straight described in the step (2-1)
Flow Line overload capacity is met：
The short-time overload capacity limit of DC current no more than DC line, i.e.,
Wherein, idcFor DC bus current, idc_maxFor the DC line short-time overload capacity limit.
8. fault traversing according to claim 2 and restoration methods, it is characterised in that the step (2-1), step (2-
2) after, following steps are also performed：
(2-3) is superimposed auxiliary voltage on the upper and lower bridge arm reference voltages of MMCMake the upper and lower bridge arm voltages of MMC
For：The superposition auxiliary voltage reduces the climbing of surge current, with
The risk that the current surge stress for avoiding transverter excessive caused by unsuccessful reclosing is brought to system safety operation；
Wherein, δ is PCC point built-in potentials evRelative to ac bus voltage usPhase difference, idcIt is (whole for failure DC bus current
Stream direction is positive direction),For DC current reference value, R (R>0) it is damped coefficient, up_upFor bridge arm voltage on MMC, up_down
For bridge arm voltage under MMC；If dc circuit breaker reclosing success, due to the presence of the flat ripple reactance of direct current, idcIt is not in wave
Gush electric current, therefore cut-off stream current reference valueIf dc circuit breaker unsuccessful reclosing, surge current idcIt is rapid to rise.
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| CN117559567A (en) * | 2024-01-11 | 2024-02-13 | 西安西电电力***有限公司 | Control method and device of multiport energy router |
| CN117559567B (en) * | 2024-01-11 | 2024-04-26 | 西安西电电力***有限公司 | Control method and device of multiport energy router |
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