CN106505642B - A kind of AC/DC decoupling control method and its application in flexible HVDC transmission system - Google Patents
A kind of AC/DC decoupling control method and its application in flexible HVDC transmission system Download PDFInfo
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- CN106505642B CN106505642B CN201610908532.4A CN201610908532A CN106505642B CN 106505642 B CN106505642 B CN 106505642B CN 201610908532 A CN201610908532 A CN 201610908532A CN 106505642 B CN106505642 B CN 106505642B
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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
- H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc networks
Abstract
The invention discloses a kind of AC/DC decoupling control methods of modularization multi-level converter, it is included in current inner loop control and increases DC current control, and DC circuit control includes positive DC current control and negative DC current control, thus the main component of the output of AC current control, the output of positive DC current control and the output of negative DC current control collectively as the output voltage reference value of each phase bridge arm of MMC；Control AC current control, the reference value and output of positive DC current control and negative DC current control, the control of the main component of the output voltage reference value to each phase bridge arm of MMC can be realized, and then can realize that inverter is latched because of bridge arm overcurrent when preventing DC Line Fault.The application that the invention also discloses the above methods in flexible HVDC transmission system.Method of the invention may insure that alternating current and DC current maintain in safe range, to realize that the DC Line Fault of aerial flexible HVDC transmission system passes through.
Description
Technical field
The invention belongs to electric system transmission & distribution electro-technical fields, more particularly, to a kind of modularization multi-level converter
AC/DC decoupling control method and its application in flexible HVDC transmission system.
Background technique
Modularization multi-level converter (Modular Multilevel Converter, MMC) technology has construction module
Change, be easy to the advantages that extending, since proposition, has been widely used in industry.By the end of currently, all throwings in the world
The MMC high voltage direct current transmission project of fortune be using based on half-bridge submodule semi-bridge type MMC technology or with half-bridge submodule
Two level of cascade (Cascaded two level, CTL) technology of (Half bridge sub-module, HBSM) homotype.But
Semi-bridge type MMC and CTL there are problems that DC Line Fault cannot be coped with.After DC Line Fault occurs for transmission line of electricity, AC system
Fault current persistently will be provided to fault point by the freewheeling diode of semi-bridge type MMC and CTL, it usually needs inverter is coupled
AC circuit breaker to cutting off direct fault current.Therefore, existing engineering mostly uses direct current cables to transmit electricity greatly to reduce
The probability that DC Line Fault occurs.
With the further development of HVDC Transmission Technology, voltage, the capacitance grade of flexible HVDC transmission system are higher and higher,
Transmission range is more and more remoter, this, which to transmit at a distance using overhead line, becomes inexorable trend.Direct current overhead transmission line failure rate compared with
Height, and be mostly transient fault, the method for cutting off direct fault current using AC circuit breaker is cut-off will substantially increase
The time of system break power supply and the time to restore electricity, jeopardize the safe and stable operation of electric system and because interruption of power supply can
It can cause heavy economic losses and social concern.
In order to cope with DC Line Fault problem, a kind of effective method is using semi-bridge type submodule and bridge-type submodule string
Mixed type MMC made of connection.Occur DC Line Fault when, by be latched mixed type MMC power electronic devices driving signal to
Direct fault current is blocked, prevents from cut-offfing AC circuit breaker.The method of above-mentioned locking requires mixed type MMC to interrupt, and
After DC Line Fault blocking, need to restart mixed type MMC, Fault Isolation time and the time that restores electricity are still longer.
In order to overcome the above problem, prevent from being latched mixed type MMC, patent document CN104300569A during DC Line Fault
Disclose the DC Line Fault traversing control method of mixed type MMC a kind of, it is characterised in that when DC Line Fault occurs, real-time monitoring is straight
Side residual voltage value is flowed, according to the alternating voltage reference value of DC voltage residual voltage value and output required for the every phase of MMC, is calculated
It obtains in every phase, the reference voltage value of upper and lower bridge arm full-bridge submodule equivalent voltage source and half-bridge submodule equivalent voltage source.
Academic paper " submodule mixed type MMC-HVDC DC Line Fault passes through control strategy " that Kong Ming et al. is delivered (Kong Ming, Tang Guangfu,
The deep pool submodule mixed type MMC-HVDC DC Line Fault of he passes through control strategy [J] Proceedings of the CSEE, and 2014,34
(30):The DC Line Fault that a kind of mixed type MMC is proposed in 5343-5351) passes through control strategy, during DC Line Fault,
By the DC component zero setting of bridge arm output voltage reference value, bridge arm output voltage is all generated by full-bridge submodule, half-bridge submodule
The number zero setting of block investment.
Scheme in CN104300569A needs to correct the ginseng of each bridge arm using the DC side residual voltage value monitored
Voltage value is examined, is substantially a kind of open loop control strategy.The scheme of Kong Ming et al. and the scheme of CN104300569 have it is similar it
Place, difference are not real-time monitoring DC side residual voltage value, but artificially setting DC side residual voltage value is zero, this two
The defect of class method is that closed-loop control can not be formed to DC current and submodule capacitor voltage, to there is generation overcurrent
Or the security risk of submodule capacitance overvoltage, actually by Figure 12 of above-mentioned paper it is found that during DC Line Fault, DC current
Value rises to instant of failure 8kA or so by the 1.6kA of stable state, and direct current overcurrent multiple is up to 5 times, will transport to the safety of inverter
Row threatens.In addition, above-mentioned prior art is not directed to pseudo- bipolar flexible direct current transmission system (or for symmetrical monopolar
Property flexible HVDC transmission system) DC Line Fault proposes effective fault traversing scheme over the ground for pole so that pseudo- bipolar flexible direct current
The operation of transmission system still has the Fault Isolation time and the time longer defect that restores electricity.
Summary of the invention
Aiming at the above defects or improvement requirements of the prior art, the present invention provides one kind be suitable for it is pseudo- it is ambipolar make somebody a mere figurehead it is soft
Property DC transmission system control method, its object is to redesign the control of existing pseudo- bipolar modules multilevel converter
Framework processed, so that during normal operation and DC Line Fault, it can be ensured that alternating current and DC current maintain safe range
It is interior, to realize that the DC Line Fault of aerial flexible HVDC transmission system passes through.
The specific technical solution of above-mentioned purpose to realize the present invention, use is as follows：
A kind of AC/DC decoupling control method of modularization multi-level converter, has output for realizing part submodule
Uninterrupted operation of the modularization multi-level converter of negative voltage ability under AC fault and/or DC Line Fault, feature exist
In the control method includes
Increase DC current control in current inner loop control, and DC circuit control includes the control of positive DC electric current
System and negative DC current control so that the current inner loop control include AC current control, positive DC current control and
Negative DC control, so that the output of the AC current control, the output of positive DC current control and cathode are straight
The output of galvanic electricity flow control collectively as each phase bridge arm of the modularization multi-level converter output voltage reference value it is main
Component；
The reference value of the AC current control, positive DC current control and negative DC current control is controlled, simultaneously
The output for controlling the AC current control, positive DC current control and negative DC current control, can be realized to described
The control of the main component of the output voltage reference value of each phase bridge arm of modularization multi-level converter, and then can realize and prevent direct current
Inverter is latched because of bridge arm overcurrent when failure.
As present invention further optimization, reference value, that is, current instruction value of the AC current control is by an outer ring
Controller generates, which is used to control the physical quantity of characterization modularization multi-level converter capacitor institute storage energy.
As present invention further optimization, the physical quantity packet of modularization multi-level converter capacitor institute storage energy
The energy storage summation of all submodule capacitors of inverter is included but is not limited to, all submodule capacitor voltage average values of inverter change
Flow the submodule capacitor voltage average value of all exportable negative levels of device or the submodule institute of all exportable negative levels of inverter
The sum of storage energy.
As present invention further optimization, the positive DC current controller and negative DC current controller it is straight
Stream reference value, that is, current instruction value is generated by outer ring controller relevant to dc power, and preferably dc power controls, is straight
The voltage-controlled system of galvanic electricity or sagging control.
As present invention further optimization, the AC current control, positive DC current control and negative DC electricity
The output of flow control is respectively inverter ac output voltage reference value, positive DC voltage reference value and negative DC voltage ginseng
Examine value, wherein
The main component of bridge arm output voltage reference value exchanges output with each phase for positive direct voltage reference value in each phase
The difference of voltage reference value, the main component of each phase lower bridge arm output voltage reference value are cathode direct voltage reference value and each intersection
Flow the sum of output voltage reference value.
As present invention further optimization, when DC Line Fault occurs, by by the positive DC current control and/
Or the output that negative DC controls quickly reduces the control realized to the main component, and then realization prevents from changing when DC Line Fault
Stream device is latched because of bridge arm overcurrent
As present invention further optimization, by the positive DC current control and/or negative DC current control
Output is quickly reduced：The integrator of corresponding positive DC current control or negative DC current control is reset, or
It is set as the lower limit of HVDC Modulation ratio, so that integrator starts to integrate under new initial value, reduces HVDC Modulation ratio, from
And reduce direct fault current.
It as present invention further optimization, monitors after DC Line Fault occurs, by by the AC current control
The absolute value of instruction value quickly reduces realization and reduces alternating current, prevents exchange side with the exchange instruction value before DC Line Fault to mould
The bridge arm charge/discharge of block multilevel converter leads to the submodule capacitor sustained overvoltage of modularization multi-level converter/owe
Pressure.
As present invention further optimization, the instruction value of the AC current control is quickly reduced it is specially：It will be sub
The integrator of module average capacitor voltage controller is reset, so that integrator starts to integrate under new initial value, is reduced
DC Line Fault exchanges active current command value after occurring.
As present invention further optimization, when only DC Line Fault occurs for anode, the positive DC current control it is straight
Stream current reference value, that is, instruction value is set as straight with the cathode of the DC current instruction value of negative DC current control or actual measurement
Galvanic electricity flow valuve is equal；When only DC control occurs for cathode, the DC current reference value of the negative DC current control is instructed
Value is set as equal with the positive DC electric current of the DC current instruction value of positive DC current control or actual measurement.
As present invention further optimization, plus earth DC Line Fault extremely occurs to pole DC Line Fault or simultaneously for generation
When being grounded DC Line Fault with cathode, positive DC current control and the DC current instruction value of negative DC current control are still protected
It holds to be generated by the outer ring controller respectively coupled.
As present invention further optimization, plus earth DC Line Fault extremely occurs to pole DC Line Fault or simultaneously for generation
When being grounded DC Line Fault with cathode, the DC current instruction value of the positive DC current control and negative DC current control is set
It is set to from AC line trackside and absorbs DC current, to quickly extinguish fault electric arc.
As present invention further optimization, failure pole occur permanent type pole over the ground DC Line Fault when, closure failure is extremely straight
Earthing switch at outflux provides fault current path by earthing switch and the earth for non-faulting pole, so that failure pole
Route is not charged, failure pole convenient to overhaul, and non-faulting pole still remains operational.
As present invention further optimization, the AC current control is based on the decoupling control under rotational coordinates, altogether
Include two control channels of active current control and reactive current control.
As present invention further optimization, bridge arm output voltage reference value also includes loop current suppression control output with reference to electricity
Negated amount is pressed, with the main component collectively as the reference value of the bridge arm output voltage.
As present invention further optimization, the loop current suppression controller includes positive loop current suppression controller and cathode
Loop current suppression controller, wherein
The calculation of circulating current method of the anode loop current suppression controller is
The calculation of circulating current method of the cathode loop current suppression controller is
Wherein idiffpj,idiffnjThe circulation of bridge arm and lower bridge arm, i respectively in jth phaseupj,idnjRespectively bridge arm in j phase
With lower bridge arm measured current value, ij_refFor the alternating current instruction value of jth phase,WithRespectively actual measurement positive DC is defeated
Electric line DC voltage over the ground and actual measurement ground are to the voltage of negative DC transmission line of electricity or are or the positive DC
Voltage reference value and negative DC voltage reference value, and rectification direction is set as alternating current positive direction, direct-flow positive pole is to direct current
Cathode circulating current is bridge arm current positive direction.
As present invention further optimization, it can also pass through the electricity of increase modularization multi-level converter (MMC) DC side
Inductance value is to reduce direct fault current.
It is another aspect of this invention to provide that providing a kind of AC/DC decoupling controlling party of above-mentioned modularization multi-level converter
Application of the method in flexible HVDC transmission system, wherein the converter station of the flexible HVDC transmission system includes part submodule
Has the modularization multi-level converter of output negative voltage ability, the part submodule has the module of output negative voltage ability
Change multilevel converter is all made of the AC/DC decoupling control method and is controlled.
As present invention further optimization, the flexible HVDC transmission system is pseudo- ambipolar aerial flexible DC transmission
System.
As present invention further optimization, the flexible HVDC transmission system is to make somebody a mere figurehead DC power transmission line, direct current
Cable or direct current cables mix the DC transmission system as transmission of electricity medium with aerial DC power transmission line.
It is another aspect of this invention to provide that providing a kind of AC/DC decoupling controlling party of above-mentioned modularization multi-level converter
Application of the method in flexible HVDC transmission system, wherein it monitors after permanent monopolar grounding fault occurs, investment failure pole
Grounding switch, the electrical isolation of shape paired fault pole, and constituted circuit by grounding switch and the earth and provided direct current for non-faulting pole
Current path
In general, control method of the invention is compared and the prior art, is had the following technical effect that：
(1) the solution of the present invention redesigned the framework of the current inner loop controller of MMC and meanwhile contain exchange it is active
Current control exchanges reactive current control, positive DC current control and four control loops of negative DC current control, thus
When ensuring generation direct current extremely to pole and direct current pole fault to ground, DC current is in slave mode, avoids power electronic devices
It is damaged during DC Line Fault because of overcurrent；
(2) for the solution of the present invention in normal operation and DC Line Fault, control logic is consistent, need to only change DC current
Instruction value, without carrying out logic switch, scheme implements more simple, also more reliable.
(3) it is inclined to generate alternating voltage in exchange side when pseudo- bipolar DC system pole fault to ground for existing controller application
It sets or DC voltage bias, threatens equipment safety, when controller stable state provided by the invention, exchanges side without DC offset voltage, if
Standby safety in operation greatly promotes.
(4) when pole fault to ground occurs for existing controller, need to interrupt the power transmission of non-faulting pole, this controller occurs
When the fault to ground of pole, non-faulting pole remains to maintain power transmission, to reduce economic loss, improves Operation of Electric Systems peace
Total stability.
Detailed description of the invention
Fig. 1 is a kind of typical bridge-type modularization multi-level converter topology in the prior art；
Fig. 2 is a kind of typical intersection cascade connection type modularization multi-level converter topology in the prior art；
Fig. 3 is the mixed type MMC topology being made of bridge-type submodule semi-bridge type submodule；
Fig. 4 is the mixed type MMC topology being made of intersection cascade connection type submodule semi-bridge type submodule；
Fig. 5 is the AC/DC decoupling control method according to modularization multi-level converter provided by one embodiment of the present invention
Structure principle chart；
Fig. 6 is the schematic illustration according to loop current suppression controller provided by one embodiment of the present invention；
Fig. 7 is that existing modularization multi-level converter typical case controls topology；
Fig. 8 is the both ends being made of the half-bridge full-bridge mixed type MMC for being suitable for the invention AC/DC decoupling control method
DC transmission system；
Fig. 9 is that the AC/DC decoupling control method of the embodiment of the present invention carries out anode permanent DC Line Fault emulation knot over the ground
Fruit schematic diagram；
Figure 10 is that the AC/DC decoupling control method of the embodiment of the present invention carries out anode instantaneity DC Line Fault emulation over the ground
Result schematic diagram；
Figure 11 is that the AC/DC decoupling control method of the embodiment of the present invention carries out extremely to extremely permanent DC Line Fault emulation knot
Fruit schematic diagram.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right
The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and
It is not used in the restriction present invention.As long as in addition, technical characteristic involved in the various embodiments of the present invention described below
Not constituting a conflict with each other can be combined with each other.
FIG. 1 to FIG. 4 is typically to be applicable to the MMC topology of control method proposed by the invention in the prior art.Such as
Shown in Fig. 1~4, wherein Fig. 1 is bridge-type MMC, and each bridge arm is connected in series by multiple full-bridge submodules.Fig. 2 is by intersecting
The MMC topology that cascade connection type submodule is constituted, each bridge arm of Fig. 2 are connected in series by multiple intersection cascade connection type submodules.Fig. 3 serves as reasons
The mixed type MMC topology that full-bridge submodule and half-bridge submodule are constituted, each of which bridge arm by multiple half-bridge submodules with it is multiple
Full-bridge submodule is connected in series.Fig. 4 is the mixed type MMC topology being made of intersection cascade connection type submodule and half-bridge submodule,
Each bridge arm is connected in series by multiple half-bridge submodules and multiple cascade submodules that intersect.Its topological common trait of above-mentioned MMC
It is that each bridge arm contains the submodule (such as full-bridge submodule and intersection cascade connection type submodule) that can export negative voltage, this hair
Bright control method is suitable for various it is known that bridge arm, which has, exports the MMC topology for continuing negative voltage ability.Bridge arm has defeated
The MMC for continuing negative voltage ability out is generally used for aerial flexible HVDC transmission system, but control method of the invention is not limited to
This, such as it is equally applicable to the flexible DC transmission system using direct current cables or direct current cables and direct current overhead line mixed connection route
System.
Each primary variables or the physical significance of abbreviation involved in various embodiments of the present invention are listed in the table below in 1.
Primary variables involved in 1 embodiment of the present invention of table, abbreviation physical significance
Fig. 5 is the control principle block schematic illustration of the control method of one embodiment of the invention, as shown in figure 5, this implementation
In example, inner ring current control is made of AC current control, DC current control and loop current suppression control.Conventional MMC control
Making its inner ring current control only includes that AC current control and loop current suppression control, and is controlled in the embodiment of the present invention in interior circular current
Middle increase DC current control.According to MMC basic theories, when bridge arm circulation is adequately suppressed, the expression formula of bridge arm current is
Iarm=idc/3+iac/2, wherein iarm, idc, iac respectively represent bridge arm current, DC current and each phase alternating current of MMC
Stream, when DC current and alternating current are controlled simultaneously, bridge arm current will be controlled in safe range, so that it is guaranteed that any work
Under condition, MMC will not be latched because of bridge arm overcurrent.
As shown in figure 5, the AC current control in the present embodiment can be further by watt current control and reactive current
Control is constituted, and DC current control is also further made of positive DC current control and negative DC current control.
As shown in figure 5, the exchange active current command value in the present embodiment is generated by exchanging active outer ring controller, this is outer
Ring controller is used for control submodule capacitance voltage average value.Submodule capacitor voltage average value can be by all submodule capacitors
The sum of voltage value obtains after being added divided by submodule total number.During being passed through due to DC Line Fault, it is straight that main investment has output
Flow negative pressure submodule, for improve controller response speed, submodule capacitor voltage average value be also possible to it is all have it is defeated
The average value of the capacitance voltage of the submodule of direct current negative pressure ability out.The exchange active current command value can also be by controlling
The outer ring controller of the gross energy of MMC storage generates.
As shown in figure 5, the DC current instruction value of the present embodiment includes positive DC current instruction value and negative DC electricity
Stream instruction value two, to independently control positive DC current value and negative DC current value.When normal operation, each direct current
Flowing instruction value can be generated by dc power outer ring or DC voltage outer ring.When pole fault to ground occurs, the direct current of failure pole
Stream instruction value is then set as the DC current instruction value of non-faulting pole, or is set as the DC current measured value of non-faulting pole,
So that the DC current of failure pole is equal with the DC current of non-faulting pole.For example, anode is controlled when DC Line Fault occurs for anode
Flag bit Fp processed sets III, so that positive DC current instruction value is equal with negative DC current instruction value, to be negative DC
Electric current provides current path, prevents grounding apparatus from flowing through DC current and jeopardizes equipment volume safety.
Bottom control includes modulation and submodule capacitor voltage Pressure and Control in Fig. 5, can use this field mature technology,
Details are not described herein.
During normal operation and DC Line Fault, AC current control and the DC current control of the embodiment of the present invention are
Identical controller is not necessarily to switch control logic, avoids control logic and is switched to the disturbance of system bring, substantially increases and be
The safety of system operation.During DC Line Fault, exchange outer loop control remain unchanged, MMC submodule energy storage can be maintained constant and with
AC system exchanges reactive power.
During pole fault to ground is passed through, when reaching stable state, failure pole is different from the DC voltage of non-faulting pole but it is flowed through
DC current it is identical, thus the dc power that is exported during DC Line Fault of failure pole and non-faulting pole and respective direct current
It is pressed into direct ratio.Since failure pole is identical as the exchange side voltage of non-faulting pole, in order to maintain upper and lower bridge arm exchange side and DC side
Power-balance, during the fault to ground of pole, alternating current also should be by the DC voltage of positive electrode and negative electrode between upper and lower bridge arm point
Match.
For this purpose, disclosing bridge arm calculation of circulating current method of the present invention in embodiment illustrated in fig. 6, (i.e. bridge arm circulation is pre-
Estimate device), wherein the circulation value of upper and lower bridge arm is subtracted by the bridge arm current value of actual measurement will flow through the fundamental frequency alternating current of the bridge arm
Instruction value and obtain, wherein flow through upper and lower bridge arm fundamental frequency alternating current instruction value be MMC alternating current instruction value by upper and lower
The size of the direct voltage reference value of bridge arm or upper and lower bridge arm actual measurement DC voltage, divides equally between upper and lower bridge arm and is obtained.
Preferably regulation rectification direction is that alternating current positive direction and direct-flow positive pole circulate to direct current cathode in the present embodiment
Electric current is bridge arm current positive direction, then the calculation of circulating current method of positive loop current suppression controller is：
The calculation of circulating current method of cathode loop current suppression controller is：
Wherein idiffpj,idiffnjThe circulation of bridge arm pole lower bridge arm, i respectively in jth phaseupj,idnjRespectively upper bridge arm with
Lower bridge arm measured current value, ij_refFor the alternating current instruction value of jth phase,WithRespectively actual measurement positive DC transmission of electricity
Voltage of the DC voltage and actual measurement ground of line-to-ground to negative DC transmission line of electricity.When defined alternating current positive direction and directly
When galvanic electricity stream positive direction is with preferably providing opposite, above-mentioned formula (1), (2) withupj,i,j_refCorresponding positive and negative number can do corresponding tune
Whole, how to adjust corresponding positive and negative number is knowledge.
In a preferred embodiment, in order to further decrease direct fault current, can after monitoring DC Line Fault,
The integrator of DC current inner loop control is reset, or is set as the lower limit of HVDC Modulation ratio, so that integrator is new
Start to integrate under initial value, reduces HVDC Modulation ratio.
It in a preferred embodiment, can be in order to reduce charge and discharge of the submodule capacitor voltage during DC Line Fault
After monitoring DC Line Fault, the integrator of submodule average capacitor voltage controller is reset, so that integrator is new
Initial value under start to integrate, reduce DC Line Fault occur after, exchange active current command value, reduce exchange side it is more to modularization
The charge/discharge effect of level converter submodule capacitor.
There are certain operating lags for DC current controller, occur to DC current controller to have started in DC Line Fault
In the time interval of effect, direct fault current will constantly increase, in order to reduce the direct fault current in this time, one
In a preferred embodiment, reduce direct fault current by increasing direct current current-limiting inductance value.
Fig. 7 gives part submodule and has the modularization multi-level converter of negative voltage fan-out capability (such as shown in Fig. 3
The mixed type MMC being made of half-bridge and full-bridge submodule) known to Typical Controller.Comparison diagram 5 and Fig. 7 are it is found that the present invention
Each embodiment scheme in more DC current controllers, and DC current controller is further subdivided into positive DC
Current controller and negative DC current controller.In order to which positive DC electric current and negative DC electric current is separately controlled, so into
One step devises the loop current suppression controller of Fig. 6.In addition, exchanging the instruction value of watt current by the average electricity of submodule in Fig. 5
Hold voltage controller to generate.
Fig. 8 is the validity schematic diagram for the control method of emulation testing various embodiments of the present invention.MMC1 in Fig. 8,
The rated direct voltage and rated power of MMC2 is each bridge arm of ± 320kV and 1000MW, MMC1 and MMC2 by 100
Full-bridge submodule is connected in series with 100 half-bridge submodules, and the voltage rating of each submodule is taken as 3.2kV, each submodule
The submodule capacitor of block is 5mF.When normal operation, MMC1 is used to control the DC port voltage of MMC1, and MMC2 is for controlling
The active power of MMC2 transmission.
Fig. 9 is the simulation result schematic diagram that permanent DC Line Fault occurs for anode.In emulation, the disturbance of setting is 2.0s
When, permanent earth fault occurs for the positive DC bus of MMC1.Positive DC voltage and the ground over the ground that Fig. 9 (a) is MMC1
To negative DC voltage, it is known that, since DC Line Fault, positive DC voltage are reduced to zero to permanent anode over the ground, negative DC electricity
The steady-state value of pressure is still maintained at 1.0pu (abbreviation of pu i.e. unit " perunit ").Fig. 9 (b) is the dc power of MMC1, it is known that is used
After controller of the invention, non-faulting pole can maintain to run, so after permanent monopole fault to ground occurs, flexible DC transmission
System is still able to maintain 50% power delivery capabilities.
Figure 10 is the simulation result diagram that instantaneity pole fault to ground occurs for anode.MMC1 positive DC bus outlet hair when 2s
Instantaneity monopolar grounding fault is given birth to, the failure is removed automatically after 0.1s.Figure 10 (a) is positive direct voltage reference value and actual measurement
Value, it is known that designed controller can make its instruction value of positive DC voltage-tracing.Figure 10 (b) is direct current of the ground to cathode
Voltage reference value and measured value.
Figure 10 (c) is the reference value and measured value schematic diagram of positive DC current, and Figure 10 (d) is the ginseng of cathode DC current
Examine value and measured value.Figure 10 (c)-(d) shows that control method of the invention can make positive DC electric current and negative DC electricity
Stream tracks respective instruction value so that it is guaranteed that direct current overcurrent does not occur for when DC Line Fault.Figure 10 (e) is the ginseng of d axis AC electric current
Examine value and measured value.Figure 10 (f) is the reference value and measured value of q axis AC electric current.Figure 10 (e)-(f) shows control of the invention
Method can accurately control alternating current.Complex chart 10 (c)-(f), since control method of the invention controls alternating current simultaneously
Stream and DC current, thus during DC Line Fault, bridge arm current will be strictly limited in safe range, such as Figure 10 (g)-(h)
It is shown.Figure 10 (g) is the bridge arm current of bridge arm in each phase of MMC1, and Figure 10 (h) is the bridge arm current of each phase lower bridge arm of MMC1.It can
To know, when normal operation, the peak value of bridge arm current is about 1.6kA, and when DC Line Fault occurs, the peak value of bridge arm current is about 2.4kA,
Only occurs for bridge arm current in 50% overcurrent of millisecond time scale the duration, not will lead to converter blocking.
Figure 10 (i) is the electric current of MMC1 AC transformer grounding point, it is known that, earth current very little will not jeopardize exchange and become
The operation of depressor.Figure 10 (j) be submodule capacitor voltage average value reference value and measured value, it is known that during DC Line Fault with therefore
After barrier restores, submodule capacitor voltage average value is controlled near rated value, and control method of the invention may insure direct current
During failure, overvoltage does not occur for the submodule of MMC.
Figure 11 (a)-(j) is the simulation result extremely to pole permanent fault.The positive DC bus of MMC2 exports hair when 2s
Raw permanent anode is shorted DC Line Fault to cathode.The physical significance of each subgraph of Figure 11 is consistent with Figure 10.Figure 11 shows the present invention
Control method when being also ensured extremely to pole DC Line Fault, make somebody a mere figurehead the safe operation of flexible HVDC transmission system.
The AC/DC decoupling control method of above-mentioned modularization multi-level converter of the invention is in flexible HVDC transmission system
In application a concrete scheme in, the converter station of the flexible HVDC transmission system includes that have output negative for part submodule
The modularization multi-level converter of voltage capability, the modular multilevel that the part submodule has output negative voltage ability change
Stream device is all made of the described in any item control methods of claim 1 to 17 and is controlled.
Preferably, flexible HVDC transmission system is pseudo- ambipolar aerial flexible HVDC transmission system, is also possible to others
To be mixed using making somebody a mere figurehead DC power transmission line, direct current cables or direct current cables with aerial DC power transmission line as transmission of electricity medium
DC transmission system.
The AC/DC decoupling control method of above-mentioned modularization multi-level converter of the invention is in flexible HVDC transmission system
In application a concrete scheme in, monitor after permanent monopolar grounding fault occurs, put into failure pole grounding switch,
The electrical isolation of shape paired fault pole, and constituted circuit by grounding switch and the earth and provided DC current path for non-faulting pole.
Using above-mentioned control method of the invention, and put into grounding switch, so that it may guarantee non-faulting pole energy continuous service, and lead to
Crossing grounding switch makes faulty line not charged, and faulty line maintenance can be realized.
The foregoing is merely those skilled in the art will readily recognize that presently preferred embodiments of the present invention, not to
The limitation present invention, any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should all include
Within protection scope of the present invention.
Claims (21)
1. it is negative to have output for realizing part submodule for a kind of AC/DC decoupling control method of modularization multi-level converter
Uninterrupted operation of the modularization multi-level converter of voltage capability under AC fault and/or DC Line Fault, which is characterized in that
The control method includes
In current inner loop control increase DC current control, and the DC circuit control include positive DC current control and
Negative DC current control, so that the current inner loop control includes AC current control, positive DC circuit control and cathode
DC control, so that the output of the AC current control, the output of positive DC current control and negative DC electricity
Main component of the output of flow control collectively as the output voltage reference value of each phase bridge arm of the modularization multi-level converter；
The reference value for controlling the AC current control, positive DC current control and negative DC current control, controls simultaneously
The output of the AC current control, positive DC current control and negative DC current control can be realized to the module
Change the control of the main component of the output voltage reference value of each phase bridge arm of multilevel converter, and then can realize and prevent DC Line Fault
When inverter be latched because of bridge arm overcurrent.
2. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 1, wherein described
The reference value of AC current control include exchange watt current reference value with exchange two components of reactive current reference value, wherein handing over
Stream watt current reference value is generated by an outer ring controller, and the outer ring controller is for controlling the characterization modular multilevel change of current
The physical quantity of device capacitor institute storage energy.
3. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 2, wherein described
The physical quantity of modularization multi-level converter capacitor institute storage energy include but is not limited to be all submodule capacitors of inverter
Energy storage summation, the submodule capacitor electricity of all submodule capacitor voltage average values of inverter, all exportable negative levels of inverter
Flatten the submodule electricity institute storage energy summation of mean value or all exportable negative levels of inverter.
4. a kind of AC/DC decoupling controlling party of modularization multi-level converter according to any one of claim 1 to 3
Method, wherein DC reference value, that is, current instruction value of the positive DC current controller and negative DC current controller is equal
It is generated by outer ring controller relevant to dc power, including dc power control, DC voltage control or sagging control.
5. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 4, wherein described
The output of AC current control, positive DC current control and negative DC current control is respectively inverter ac output voltage
Reference value, positive DC voltage reference value and negative DC voltage reference value, wherein
The main component of bridge arm output voltage reference value is positive direct voltage reference value and each phase ac output voltage in each phase
The difference of reference value, the main component of each phase lower bridge arm output voltage reference value exchange for cathode direct voltage reference value with each phase defeated
The sum of voltage reference value out.
6. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 5, wherein sending out
When raw DC Line Fault, by the way that the output of the positive DC current control and/or negative DC control is quickly reduced realization pair
The control of the main component, and then realizing prevents inverter when DC Line Fault to be latched because of bridge arm overcurrent.
7. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 6, wherein by institute
The output for stating positive DC current control and/or negative DC current control, which is quickly reduced, is specially：By corresponding positive DC
The integrator of current control or negative DC current control is reset, or is set as the lower limit of HVDC Modulation ratio, so that integral
Device starts to integrate under new initial value, reduces HVDC Modulation ratio, to reduce direct fault current.
8. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 7, wherein monitoring
To after occurring DC Line Fault, by the way that the instruction value of the AC current control quickly to be reduced to the control realized to the main component
System, and then realizing prevents exchange side from giving bridge arm charge/discharge, causes submodule capacitor voltage overvoltage/under-voltage.
9. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 8, wherein by institute
The output for stating AC current control, which is quickly reduced, is specially：The integrator of submodule average capacitor voltage controller is reset, from
And integrator is made to start to integrate under new initial value, reduce after DC Line Fault occurs and exchanges active current command value.
10. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 9, wherein only
When DC Line Fault occurs for anode, DC current reference value, that is, instruction value of the positive DC current control is set as straight with cathode
The DC current instruction value of galvanic electricity flow control or the negative DC current value of actual measurement are equal；When only DC control occurs for cathode,
DC current reference value, that is, instruction value of the negative DC current control is set as the direct current with positive DC current control
The positive DC electric current for flowing instruction value or actual measurement is equal.
11. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 10, wherein hair
When plus earth DC Line Fault and cathode ground connection DC Line Fault extremely occur to pole DC Line Fault or simultaneously for life, by positive DC electricity
Flow control is maintained as being produced by the outer ring controller respectively coupled with the DC current instruction value of negative DC current control
It is raw.
12. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 11, wherein hair
When plus earth DC Line Fault and cathode ground connection DC Line Fault extremely occur to pole DC Line Fault or simultaneously for life, the positive DC
The DC current instruction value of current control and negative DC current control is set as absorbing DC current from AC line trackside, thus
Quickly extinguish fault electric arc.
13. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 12, wherein therefore
Hinder pole occur permanent type pole over the ground DC Line Fault when, the earthing switch in failure pole direct current exit is closed, by earthing switch and big
Ground provides fault current path for non-faulting pole.
14. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 13, wherein institute
Stating AC current control is based on the decoupling control under rotational coordinates, altogether includes active current control and reactive current control two
Control channel.
15. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 14, wherein bridge
Arm output voltage reference value also includes the loop current suppression control negated amount of output reference voltage, common with the main component
Reference value as the bridge arm output voltage.
16. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 15, wherein institute
Stating loop current suppression controller includes positive loop current suppression controller and cathode loop current suppression controller, wherein
The calculation of circulating current method of the anode loop current suppression controller is
The calculation of circulating current method of the cathode loop current suppression controller is
Wherein idiffpj,idiffnjThe circulation of bridge arm and lower bridge arm, i respectively in jth phaseupj,idnjRespectively in jth phase bridge arm with
Lower bridge arm measured current value, ij_refFor the alternating current instruction value of jth phase,WithRespectively actual measurement positive DC transmission of electricity
Voltage or the positive DC Voltage Reference of the DC voltage and actual measurement ground of line-to-ground to negative DC transmission line of electricity
Value and negative DC voltage reference value, and rectification direction is set as alternating current positive direction, direct-flow positive pole circulates to direct current cathode
Electric current is bridge arm current positive direction.
17. a kind of AC/DC decoupling control method of modularization multi-level converter according to claim 16, wherein also
It can be by increasing the inductance value of modularization multi-level converter DC side to reduce direct fault current.
18. the AC/DC decoupling control method of modularization multi-level converter described in any one of claims 1 to 17 is soft
Application in property DC transmission system, wherein the converter station of the flexible HVDC transmission system include part submodule have it is defeated
How electric the modularization multi-level converter of negative voltage ability out, the modularization that the part submodule has output negative voltage ability be
Flat inverter is all made of the described in any item control methods of claim 1 to 17 and is controlled.
19. application according to claim 18, wherein the flexible HVDC transmission system is pseudo- ambipolar aerial flexibility
DC transmission system.
20. according to its application described in 18 or 19 of right, wherein the flexible HVDC transmission system is to make somebody a mere figurehead DC transmission line
Road, direct current cables or direct current cables mix the DC transmission system as transmission of electricity medium with aerial DC power transmission line.
21. the AC/DC decoupling control method of modularization multi-level converter described in any one of claims 1 to 17 is soft
Property DC transmission system in application, wherein monitor after permanent monopolar grounding fault occurs, put into failure pole earthing
Lock, the electrical isolation of shape paired fault pole, and circuit is constituted by grounding switch and the earth and provides direct current circulation for non-faulting pole
Road.
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| CN108832649B (en) * | 2018-06-05 | 2021-08-27 | 天津大学 | Operating point optimization-based true bipolar flexible direct-current power grid coordination control method |
| CN109800381B (en) * | 2019-03-22 | 2020-09-18 | 清华大学 | Direct-current short-circuit current calculation method and system of modular multilevel converter |
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