CN104821711A - Modularized multilevel flexible DC power transmission current converter starting method - Google Patents
Modularized multilevel flexible DC power transmission current converter starting method Download PDFInfo
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Abstract
The invention relates to a modularized multilevel flexible DC power transmission current converter starting method comprising the following steps that A. the DC side poles of all converter stations are connected, the submodules of all the stations are locked, and the AC switch of an active station is closed so as to enter an uncontrollable charging stage; B. after voltage of the submodules of all the converter stations is higher than respectively corresponding charging threshold voltage, a controllable voltage equalizing charging method is switched on by the converter stations respectively and a controllable charging stage is initiated, and the AC side soft starting resistor of the active station is removed simultaneously; and C. a closed-loop voltage equalizing charging method is respectively switched on by all the converter stations according to the voltage situation of the AC and DC sides, and when voltage of the submodules of the converter stations is rated and stable, the converter stations are unlocked respectively and enter the unlock operation stage. The closed-loop charging mode is additionally arranged after controllable charging so that removal number can be adjusted in real time according to current voltage of the submodules, voltage of the submodules can be stabilized at the rated value via closed-loop control, and thus electrical impact in unlock operation can be avoided.
Description
Technical field
The present invention relates to a kind of modular multi-level flexible direct-current transmission converter starting method.
Background technology
Multi-end flexible direct current transmission can realize multiple feed, many drop points are powered, be in electric power system one flexibly, reliably, power transmission mode efficiently.And modularization multi-level converter because its output voltage waveforms quality is high, switching loss is low, be easy to dilatation and the advantage such as fault ride-through capacity is strong, become the trend of Multi-end flexible direct current transmission development gradually.
Completing smoothly of start-up course is the prerequisite normally run of multi-terminal system and basis, and suitable startup strategy should be able to start sequential to each converter of multi-terminal system and carry out coordinations and configure, and suppressing the electrical impact that it produces because influencing each other, avoiding starting unsuccessfully.But MMC-MTDC DC capacitor is dispersed in each submodule, it starts the equalizing charge problem not only will considering each submodule electric capacity of inverter inside, also needs to consider that between current conversion station, direct-current coupling is on the impact of MMC start-up course.
Therefore, research MMC-MTDC system coordination starts control strategy, solves submodule precharge in current conversion station and all to press and these two key issues of orderly unblock between current conversion station just seem particularly important.
But at present, research is started to MMC-MTDC system coordination both at home and abroad less.In the converter submodule precharge of multi-terminal system all in pressure, some scholars proposes to carry out the controlled stage charging of submodule by double-closed-loop control, the now startup of the power free current conversion station of AC (abbreviation passive station) requires that AC has the soft resistance that opens of the interchange of the current conversion station of power supply (abbreviation has source station) to drop into always, increase the soft demand opening resistance average power, and direct voltage can be caused to fall when unlocking; Also have scholar to devise the controlled stage starting method of phase-shifting carrier wave, but control realization is complicated; Also have scholar to propose a kind of half locking charging method, submodule can be charged to rated value, but consideration comprehensively and research are not done to converter precharge mode.Between current conversion station in orderly unblock, existing research mainly focuses on the startup strategy of source station, or the orderly unblock scheme of Converter DC-side charging, do not relate to alternating current-direct current side mixed charged situation in multi-terminal system, and the orderly unblock between the many current conversion stations of multi-terminal system is not furtherd investigate.
Application number be 201210462977.6 Chinese patent application " a kind of starting method of modular multi-level flexible direct-current transmission converter " disclose a kind of scheme.The key step of the method is: in start-up course, sorts to each submodule on brachium pontis, several submodules that excision voltage is higher, and charges to all the other submodules; And constantly repeat above process until be charged to stable state.
The method has following defect:
The first, above-mentioned charging method is a kind of controllable aerating method for electrically, only excises the submodule of fixed number (theoretical excision number).And in Practical Project, during charging stable state, impact due to factors such as circuit and submodule loss, stray parameters can make the submodule voltage deviation rated value obtained according to theory excision numerical control, the equivalent valve side alternating voltage then obtained by current sub-block voltage is different from actual alternating voltage, because lack enough large damping element in circuit, larger impulse current will be caused.
The second, precharge early stage, submodule voltage is lower, and adopting the submodule of automatic electricity getting mode to control power supply cannot work, and therefore submodule can only locking, carries out not controlled charging.According to the difference of converter AC and DC side power supply, converter has different charge circuits, to the supply voltage difference that brachium pontis or facies unit charge under each loop, cause submodule steady state voltage different, also charging threshold voltage is determined different, if charging threshold voltage arranges arbitrarily, then can cause indivedual station too early, even cannot enter the controlled charging stage slowly, correspondence causes larger electrical impact, increase even to cause start-up time and start unsuccessfully.Meanwhile, if do not distinguish charge mode in the controlled stage, excision number arranges arbitrarily, then submodule can be caused to charge different, can not reach charging requirement, even cause submodule excessive pressure damages.
3rd, in multi-terminal system, have and only have one to stand as constant DC voltage control.Multi-terminal system runs needs galvanic current pressure, if have Converter Station to unlock prior to constant DC voltage control station to run, then it injects to DC line or extracts to gain merit and direct voltage can be caused to raise or reduce, and is unfavorable for running controlling, and even causes the system failure.
Summary of the invention
The object of this invention is to provide a kind of modular multi-level flexible direct-current transmission converter starting method, in order to solve the problem one, unlock the problem that can produce greater impact electric current when running.
For achieving the above object, the solution of the present invention comprises:
A kind of modular multi-level flexible direct-current transmission converter starting method, comprises step as follows:
A, each current conversion station direct current side pole connect, and the submodule locking of each station, has source station to close alternating-current switch simultaneously, enter the not controlled charging stage;
B, each current conversion station drop into respectively after its submodule voltage is higher than each self-corresponding charging threshold voltage controlledly all presses charging method, enters the controlled charging stage, and have source station to excise AC is soft opens resistance simultaneously;
C, each current conversion station according to AC and DC side voltage condition, respectively drop into closed loop all press charging method, when its submodule voltage reach specified and stable after, unlock respectively, enter unlock the operation phase.
Further, in above-mentioned steps C, when station prosecutor formula be the current conversion station AC and DC side voltage of constant DC voltage control all stable after, this station is dropped into closed loop and is all pressed charging method; When its submodule voltage reach specified and stable after, this station unlocks pulse, and starts with the DC voltage control of slope controller, enters and unlocks the operation phase;
When all the other respectively station DC-side Voltage Stabilizations after rated value, drop into closed loop respectively and all press charging method, when its submodule voltage reach specified and stable after, unlock respectively, enter and unlock the operation phase.
Further, in the not controlled charging stage, according to AC and DC side power conditions, AC precharge, DC side precharge or the mixing precharge of alternating current-direct current side is dropped into respectively:
Under AC precharge mode, MMC ceiling for accumulation voltage is u
ij(i, j=a, b, c, i ≠ j), the lower brachium pontis of i phase and pipe fly-wheel diode conducting on brachium pontis submodule in j phase, for its submodule charges;
Under DC side precharge mode, MMC direct voltage u
pnfor all submodules of a, b, c three-phase charge simultaneously;
Under alternating current-direct current side mixing precharge mode, the line voltage u that MMC is the highest
ijwith direct voltage u
pnbe brachium pontis and brachium pontis submodule charging in j phase under i phase together, all the other brachium pontis then no current.
Further, in the not controlled charging stage, judge to exchange valve side line voltage peak u
lsize, and and u
pncompare, thus determine precharge mode:
Work as u
l>=u
pntime, be AC precharge mode;
Work as u
l=0 and u
pnwhen ≠ 0, it is DC side precharge mode;
Work as 0<u
l<u
pntime, be alternating current-direct current side mixing precharge mode.
Further, described charging threshold voltage is higher than the upper piezoelectric voltage making submodule driving power reliably power on, and for there being source station, described charging threshold voltage is lower than u
l/ N; To passive station, described charging threshold voltage is lower than u
pn/ 2N; A brachium pontis has N number of submodule, and exchanging valve side line voltage peak is u
l.
Further, controlledly all press charging method: each control cycle, to under AC precharge mode or alternating current-direct current side mixing precharge mode, N number of submodule in the MMC brachium pontis of participation charging, or MMC facies unit 2N submodule of DC side precharge mode sorts according to voltage, under m the submodule that trigger voltage is the highest, pipe IGBT conducting makes it be in excision state, and all the other submodules keep blocking simultaneously; The controlled excision number m all pressing charging method to determine
refcomputational methods are as follows, and wherein round is round function, and MMC submodule rated voltage is U
sm:
Further, described closed loop all presses charging method to be controlledly all press charging method based on described, according to closed-loop control result adjustment submodule excision number; Closed-loop control is with submodule rated voltage for input, and with submodule virtual voltage for feedback, output sub-module excises number adjustment amount.
Further, MMC submodule rated voltage U
smwith actual value u
smdeviation delta u
smbe ± Δ U through a threshold voltage
smhysteresis comparator, obtain excision number adjustment amount Δ m, by Δ m through an initial value be the controlled excision number m all pressing charging method to determine
ref, time constant is the integral controller of τ and rounds output, finally excised number; Described hysteresis comparator control logic is:
1) as Δ usm >=Δ Usm, Δ m=1;
2) as Δ usm≤-Δ Usm, Δ m=-1;
3) otherwise, Δ m is constant.
By increasing closed loop charging modes after controlled charging, excision number can be adjusted in real time according to current sub-block voltage, submodule voltage is stabilized in rated value by closed-loop control, avoid the electrical impact unlocked when running.
At not controlled charging stage clearly each converter charge mode, can obtain inductive charging threshold voltage according to different mode, be beneficial to converter and carry out charge mode conversion in good time.Simultaneously according to the difference of not controlled charging stage charge mode and station prosecutor formula, calculate corresponding theory excision number in the controlled charging stage, can guarantee that each converter submodule both be charged near rated value, realize reliably, effectively starting control.
First constant DC voltage control station unlocks can stable DC busbar voltage, guarantees the stable operation of multi-terminal system.And in the controlled charging later stage, the AC and DC side voltage at constant DC voltage control station is all stable means that this station submodule charging is in stable state, the DC voltages at all the other stations are specified and stablely mean that all the other station submodule voltages chargings are in stable state, now drop into closed loop charging to control, submodule voltage and rated value are comparatively close, then excise number adjustment less, its fluctuation can be avoided to cause submodule to charge unstable.
Accompanying drawing explanation
Fig. 1 is three end MMC-MTDC system schematic of embodiment 1;
Fig. 2 is the MMC precharge mode identification process figure of embodiment 1;
Fig. 3-a, 3-b, 3-c are the precharge circuit diagram under not controlled charging stage three kinds of precharge modes of embodiment 1;
Fig. 4 is that the MMC closed loop of embodiment 1 all presses charging control principle drawing;
Fig. 5 is the MMC-MTDC system coordination Booting sequence schematic diagram of embodiment 1; 1. ~ be 5. start-up course redirect condition; 1. respectively to stand startup; 2. minimum submodule voltage is higher than charging threshold voltage U
t; 3. AC and DC side voltage is all stable; 4. direct voltage is specified and stable; 5. submodule is charged to specified and stable;
Fig. 6 is that three end MMC-MTDC system coordinations of embodiment 1 start simulation waveform.
Embodiment
In following embodiment, be all described for the MMC-MTDC system shown in Fig. 1.Fig. 1 is three end MMC-MTDC systems.MMC1 and MMC3 is for there being source station in definition, adopts constant DC voltage control respectively and determine AC power to control, and MMC2 is passive station, and employing is determined alternating voltage and controlled.Certainly, method of the present invention is not only adapted to three end systems, also can be applied directly to the multi-terminal system of more than three ends.In multi-terminal system, have and only have one to stand as constant DC voltage control.
As shown in Figure 3, MMC1, MMC2, MMC3 all comprise 6 brachium pontis, and it is U that single brachium pontis comprises N number of rated voltage
smsemibridge system submodule, exchanging valve side line voltage peak is u
l, DC bus-bar voltage is u
pn, rated value is U
dc.Parameter is as table 1.
Table 1
Semibridge system submodule has three kinds of operating states such as input (upper pipe IGBT conducting, lower pipe IGBT turns off), excision (upper pipe IGBT turns off, lower pipe IGBT conducting) and locking (upper, lower tube IGBT all turns off).
Except semibridge system submodule, as other execution modes, MMC also can adopt the structures such as H bridge topology.
Embodiment 1
Modular multi-level flexible direct-current transmission converter starting method, comprises step as follows:
A, each current conversion station direct current side pole connect, and the submodule locking of each station, has source station to close alternating-current switch simultaneously, enter the not controlled charging stage;
B, each current conversion station drop into respectively after its submodule voltage is higher than each self-corresponding charging threshold voltage controlledly all presses charging method, enters the controlled charging stage, and have source station to excise AC is soft opens resistance simultaneously;
C, when station prosecutor formula be the current conversion station AC and DC side voltage of constant DC voltage control all stable after, this station is dropped into closed loop and is all pressed charging method; When its submodule voltage reach specified and stable after, this station unlocks pulse, and starts with the DC voltage control of slope controller, enters and unlocks the operation phase;
D, when all the other respectively station DC-side Voltage Stabilizations after rated value, drop into closed loop respectively and all press charging method, when its submodule voltage reach specified and stable after, unlock respectively, enter and unlock the operation phase.
From whole process, each current conversion station is successively through controlled charging stage, controlled charging stage and closed loop all do not press charging so that unlock operation; And first the current conversion station that prosecutor formula of standing is constant DC voltage control enters and unlocks the operation phase.Below the principle of each step above-mentioned and the course of work are described in detail.
Not controlled charging stage described in steps A, MMC is according to AC and DC side power conditions, drop into AC precharge, DC side precharge or the mixing precharge of alternating current-direct current side respectively, the concrete identification process of these three kinds of precharge modes as shown in Figure 2: each control cycle, judges u
lsize, and and u
pncompare, thus determine precharge mode:
Work as u
l>=u
pntime, be AC precharge mode;
Work as u
l=0 and u
pnwhen ≠ 0, it is DC side precharge mode;
Work as 0<u
l<u
pntime, be alternating current-direct current side mixing precharge mode.
Under AC precharge mode, MMC ceiling for accumulation voltage is u
ij(i, j=a, b, c, i ≠ j), then brachium pontis and pipe anti-paralleled diode conducting under the lower brachium pontis submodule of j phase in i phase, makes DC bus-bar voltage be u
ij, and the lower brachium pontis of i phase and pipe fly-wheel diode conducting on brachium pontis submodule in j phase, for its submodule charges, other phase capacitor charging situations are similar.
Under DC side precharge mode, MMC direct voltage u
pnfor all submodules of a, b, c three-phase charge simultaneously.
Under alternating current-direct current side mixing precharge mode, the line voltage u that MMC is the highest
ijwith direct voltage u
pnbe brachium pontis and brachium pontis submodule charging in j phase under i phase together, all the other brachium pontis then no current.
Not during controlled charging stage stable state, according to Fig. 3, charged form calculates, and under described three kinds of charging modes, submodule voltage is as follows, all less than rated value:
Specific to three end systems of Fig. 1, because MMC1 exchanges valve side line voltage peak u
l1=290kV, exchanges valve side line voltage peak u higher than MMC3
l3=288kV, therefore controlled charging stage DC bus-bar voltage is not u
pn=u
l1, after MMC1 unlocks operation, DC bus-bar voltage is U
dc=400kV.The present invention shown in composition graphs 2 coordinates to start MMC precharge mode identification process in control strategy, then MMC1 is AC precharge mode, and MMC2 is DC side precharge mode, and MMC3 is alternating current-direct current side mixing precharge mode.Before MMC1 unlocks, due to direct voltage and MMC3 AC voltage phase difference not quite, the mixed charged phenomenon of MMC3 can not be too obvious.
Controlled charging stage MMC1, MMC2 and MMC3 precharge loop is not respectively as shown in Fig. 3-a, 3-b and 3-c.All u is supposed in figure
abfor the current maximum line voltage in each station.
In Fig. 3-a, from the turn-on condition of power model fly-wheel diode, in a phase, brachium pontis and pipe fly-wheel diode conducting on the submodule of the lower brachium pontis of b phase, make DC bus-bar voltage be u
abpeak value u
l1, the lower brachium pontis of a phase and pipe fly-wheel diode conducting on the submodule of brachium pontis in b phase simultaneously, be its submodule capacitor charging, the capacitor charging situation of other phases is similar.
In Fig. 3-b, DC bus-bar voltage u
l1for three all submodules of facies unit of MMC charge simultaneously.
In Fig. 3-c, DC bus-bar voltage u
l1valve side line voltage u is exchanged with MMC
abseries aiding connection is the lower brachium pontis of a phase and brachium pontis submodule capacitor charging in b phase, now brachium pontis and the then no current circulation of the lower brachium pontis of b phase in a phase.
Not during controlled charging stage stable state, three station submodule voltages are respectively: u
sm1=u
l1/ N=0.67pu, u
sm2=u
l1/ 2N=0.34pu, u
sm3=(u
l1+ u
l2)/2N=0.67pu, all cannot reach rated value, and the voltage of MMC2 is about the half of MMC1 and MMC3.
The controlled charging stage described in step B, (submodule voltage is submodule minimum voltage to submodule voltage here, as other execution modes, also can select as average voltage) controlledly all press charging method higher than dropping into respectively after charging threshold voltage, enter the controlled charging stage.
Charging threshold voltage is used to distinguish MMC not controlled charging stage and the controlled charging stage, should a little less than u for source station for having
l/ N, passive station is then a little less than u
pn/ 2N, simultaneously also should higher than the upper piezoelectric voltage making submodule driving power reliably power on.
Controlled charging method object of all pressing is to realize the lifting of submodule voltage and ensures electric voltage equalization between submodule, by excising a part of submodule to reduce the submodule electric capacity number sealed in charge circuit, all press to realize submodule, the part submodule choosing voltage in loop under each control cycle higher excises simultaneously.Concrete grammar is: each control cycle, to under AC precharge mode or alternating current-direct current side mixing precharge mode, in the MMC brachium pontis of participation charging, N number of submodule is (see Fig. 3-a, Fig. 3-c), or MMC facies unit 2N submodule of DC side precharge mode is (see Fig. 3-b, facies unit is corresponding upper and lower two brachium pontis) sort according to voltage, under m the submodule that trigger voltage is the highest, pipe IGBT conducting makes it be in excision state, and all the other submodules keep blocking simultaneously.Described excision number m starts to rise to theoretical value m gradually from zero
ref, described theory excision number m
refcomputational methods are as follows, and wherein round is round function:
Controlled setting of all pressing the method for charging key to be to excise quantity, as other execution modes, also background technology Literature (application number 201210462977.6) can be adopted not distinguish like that the method for precharge mode, also or other excision modes.
Specific to the system of Fig. 1, MMC1, MMC3 these two have the charging threshold voltage of source station and passive station MMC2 to be set to 1000V and 530V respectively.Because MMC1 is constant DC voltage control station, first it will unlock operation, specified in order to make submodule be charged to by AC power, and the brachium pontis submodule theory excision number of MMC1 is set to 89 according to its computing formula.MMC2 and MMC3 DC bus-bar voltage before unblock has reached stable, makes u in Fig. 3-b and Fig. 3-c
pn=U
dc, therefore, for the MMC2 of inactive side precharge mode, its facies unit submodule theory excision number is 290, and for the MMC3 of alternating current-direct current side mixing precharge mode, its brachium pontis submodule theory excision number is 55.
Described in step C, D, closed loop all presses charging method, is all to press charging method based on the controlled of excision setting number submodule number, according to closed-loop control result adjustment submodule excision number; Closed-loop control is with submodule rated voltage for input, and with submodule virtual voltage for feedback, output sub-module excises number adjustment amount.
Specific strategy is: by MMC submodule rated voltage U
smwith actual value u
smdeviation delta u
smbe ± Δ U through a threshold voltage
smhysteresis comparator, obtain excision number adjustment amount Δ m, by Δ m through an initial value be m
ref, time constant is the integral controller of τ and rounds output, finally excised number.Described hysteresis comparator control logic is:
1) as Δ usm >=Δ Usm, Δ m=1;
2) as Δ usm≤-Δ Usm, Δ m=-1;
3) otherwise, Δ m is constant.
Described integral controller timeconstantτ can between several ms to several seconds value, as τ=1.Described stagnant ring threshold voltage can use following formula approximate calculation:
Stagnant ring threshold voltage is relevant with precharge mode.Integral controller timeconstantτ can between several ms to several seconds value.The threshold voltage of hysteresis comparator can be used as 10V.
Below not controlled charging stage, controlled charging stage and the closed loop charging stage, they are separate.And each process is made up of some control cycles, not controlled charging method similar to Figure 2, all compares at each control cycle, judge, performs.
In the present embodiment, by increasing closed loop charging modes after controlled charging, excision number can be adjusted in real time according to current sub-block voltage, submodule voltage is stabilized in rated value by closed-loop control, avoid the electrical impact unlocked when running.
At not controlled charging stage clearly each converter charge mode, can obtain inductive charging threshold voltage according to different mode, be beneficial to converter and carry out charge mode conversion in good time.Simultaneously according to the difference of not controlled charging stage charge mode, calculate corresponding theory excision number in the controlled charging stage, can guarantee that each converter submodule both be charged near rated value, realize reliably, effectively starting control.
First constant DC voltage control station unlocks can stable DC busbar voltage, guarantees the stable operation of multi-terminal system.And in the controlled charging later stage, the AC and DC side voltage at constant DC voltage control station is all stable means that this station submodule charging is in stable state, the DC voltages at all the other stations are specified and stablely mean that all the other station submodule voltages chargings are in stable state, now drop into closed loop charging to control, submodule voltage and rated value are comparatively close, then excise number adjustment less, its fluctuation can be avoided to cause submodule to charge unstable.
The coordination of the present embodiment according to Fig. 5 starts control strategy, arranging emulation material time point is: start three stations during 0s, closed each station DC switch, three station submodule pulse blockings simultaneously, closed MMC1 and MMC3 alternating-current switch, enters the not controlled charging stage simultaneously; During 10s, MMC1 all presses charging two kinds of patterns to be charged to specified by its submodule by the charging of controlled all pressures and closed loop, unlocks MMC1 for this reason, makes it carry out the control of direct voltage slope; During 13s, MMC2 and MMC3 submodule voltage all presses the effect of charging method to be issued to rated value at rated direct voltage and closed loop, unlocks MMC2 and MMC3 for this reason; During 14s, the instruction slope of MMC2 and MMC3 is increased, make it enter normal operating condition.As shown in Figure 6, in figure, each amount is perunit value to simulation result, and submodule voltage chooses each 1 submodule of a phase upper and lower bridge arm.
As seen from Figure 6, in not controlled charging stage, the MMC1 being in AC precharge mode be in the MMC3 mixing precharge mode and charge similar, charge value is about 2 times of the MMC2 of DC side precharge mode, consistent with theory analysis.After the submodule voltage reaching 1000V threshold voltage and MMC2 respectively when the submodule voltage of MMC1 and MMC3 reaches 530V threshold voltage, three stations enter the controlled charging stage automatically, MMC1 and MMC3 excision is simultaneously soft opens resistance.After entering the controlled charging stage, three stand in controlled all press charging method and closed loop all to press the control of charging method under excise submodule gradually, charge rate increases, MMC1 submodule voltage is raised to rated value, MMC2 and MMC3 submodule voltage then stabilizes to 0.71pu and 0.83pu respectively because DC bus-bar voltage does not reach rated value.During 10s, MMC1 unlocks, and slope rises in DC bus voltage following instruction subsequently, finally stabilizes to specified, and meanwhile, MMC2 and MMC3 submodule voltage follow rises, and all presses the effect of charging strategy to be issued to rated value in the excitation of direct voltage and closed loop.During 13s, MMC2 and MMC3 unlocks and runs, and starts slope respectively at 14s and control alternating voltage and AC power until reach set point.
It seems from simulation result, in three current conversion station start-up courses, time cooperation is good, can carry out equalizing charge according to plan, and ensure that in start-up course, voltage and rush of current meet the demands to submodule.As can be seen here, the MMC-MTDC system coordination startup control strategy of the present invention's design is effective, feasible.
The MMC-MTDC system coordination that the present embodiment proposes starts control strategy, automatically can adapt to the various precharge mode of MMC and submodule voltage is charged to rated value, lay the foundation for MMC smoothly unlocks, effectively suppress electrical impact in start-up course by unblock scheme orderly between multi-terminal system station and direct voltage slope control mode simultaneously, realize the startup of multi-terminal system quick and stable.
Embodiment 2
Modular multi-level flexible direct-current transmission converter starting method, comprises step as follows:
A, enter the not controlled charging stage: controlled charging process does not adopt the not controlled charging method of prior art, that is, different charge modes is not set according to the difference of stream device AC and DC side power supply.
B, drop into when arriving certain voltage threshold voltage and controlledly all press charging method, enter the controlled charging stage.For each submodule, above-mentioned voltage threshold voltage value is identical.
C, when station prosecutor formula be the current conversion station AC and DC side voltage of constant DC voltage control all stable after, this station is dropped into closed loop and is all pressed charging method; When its submodule voltage reach specified and stable after, enter unlock the operation phase;
D, when all the other respectively station DC-side Voltage Stabilizations after rated value, drop into closed loop respectively and all press charging method, when its submodule voltage reach specified and stable after, unlock respectively, enter and unlock the operation phase.
Closed loop is all pressed in charging method, adopts hysteresis comparator, owing to not distinguishing precharge mode, and Δ U
smbe set to a definite value.Or stagnant chain rate is replaced with pi regulator more by force.
According to simulation result, this method is also feasible, adjusts excision number in real time according to current sub-block voltage, and submodule voltage is stabilized in rated value by closed-loop control, avoids the electrical impact unlocked when running.
Embodiment 3
In the present embodiment, also not controlled charging stage, controlled charging stage and closed loop charging stage is experienced, distinguish with embodiment 2 and be only, closed loop charges to unlock and runs, do not distinguish constant DC voltage control station and other current conversion stations, each current conversion station exchanges according to self, DC side situation determines that dropping into closed loop all presses charging method, until unlock.According to simulation result, this mode can realize submodule voltage to be stabilized in rated value by closed-loop control substantially, but easily generation system is unstable.
Be presented above three execution modes that the present invention is concrete, but the present invention is not limited to described execution mode.Under the thinking that the present invention provides; the mode easily expected to those skilled in the art is adopted to convert the technological means in above-described embodiment, replace, revise; and the effect played goal of the invention that is substantially identical with the relevant art means in the present invention, that realize is also substantially identical; the technical scheme of such formation is carried out fine setting to above-described embodiment and is formed, and this technical scheme still falls within the scope of protection of the present invention.
Claims (9)
1. a modular multi-level flexible direct-current transmission converter starting method, is characterized in that, comprises step as follows:
A, each current conversion station direct current side pole connect, and the submodule locking of each station, has source station to close alternating-current switch simultaneously, enter the not controlled charging stage;
B, each current conversion station drop into respectively after its submodule voltage is higher than each self-corresponding charging threshold voltage controlledly all presses charging method, enters the controlled charging stage, and have source station to excise AC is soft opens resistance simultaneously;
C, each current conversion station according to AC and DC side voltage condition, respectively drop into closed loop all press charging method, when its submodule voltage reach specified and stable after, unlock respectively, enter unlock the operation phase.
2. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 1, is characterized in that,
In above-mentioned steps C, when station prosecutor formula be the current conversion station AC and DC side voltage of constant DC voltage control all stable after, this station is dropped into closed loop and is all pressed charging method; When its submodule voltage reach specified and stable after, this station unlocks pulse, and starts with the DC voltage control of slope controller, enters and unlocks the operation phase;
When all the other respectively station DC-side Voltage Stabilizations after rated value, drop into closed loop respectively and all press charging method, when its submodule voltage reach specified and stable after, unlock respectively, enter and unlock the operation phase.
3. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 1, it is characterized in that, in the not controlled charging stage, according to AC and DC side power conditions, drop into AC precharge, DC side precharge or the mixing precharge of alternating current-direct current side respectively:
Under AC precharge mode, MMC ceiling for accumulation voltage is u
ij(i, j=a, b, c, i ≠ j), the lower brachium pontis of i phase and pipe fly-wheel diode conducting on brachium pontis submodule in j phase, for its submodule charges;
Under DC side precharge mode, MMC direct voltage u
pnfor all submodules of a, b, c three-phase charge simultaneously;
Under alternating current-direct current side mixing precharge mode, the line voltage u that MMC is the highest
ijwith direct voltage u
pnbe brachium pontis and brachium pontis submodule charging in j phase under i phase together, all the other brachium pontis then no current.
4. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 3, is characterized in that, not the controlled charging stage, judges to exchange valve side line voltage peak u
lsize, and and u
pncompare, thus determine precharge mode:
Work as u
l>=u
pntime, be AC precharge mode;
Work as u
l=0 and u
pnwhen ≠ 0, it is DC side precharge mode;
Work as 0<u
l<u
pntime, be alternating current-direct current side mixing precharge mode.
5. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 4, it is characterized in that, described charging threshold voltage is higher than the upper piezoelectric voltage making submodule driving power reliably power on, and for there being source station, described charging threshold voltage is lower than u
l/ N; To passive station, described charging threshold voltage is lower than u
pn/ 2N; A brachium pontis has N number of submodule, and exchanging valve side line voltage peak is u
l.
6. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 5, it is characterized in that, controlledly all press charging method: each control cycle, to under AC precharge mode or alternating current-direct current side mixing precharge mode, N number of submodule in the MMC brachium pontis of participation charging, or MMC facies unit 2N submodule of DC side precharge mode sorts according to voltage, under m the submodule that trigger voltage is the highest, pipe IGBT conducting makes it be in excision state, and all the other submodules keep blocking simultaneously; The controlled excision number m all pressing charging method to determine
refcomputational methods are as follows, and wherein round is round function, and MMC submodule rated voltage is U
sm:
7. a kind of modular multi-level flexible direct-current transmission converter starting method according to any one of claim 1-6, it is characterized in that, described closed loop all presses charging method to be controlledly all press charging method based on described, according to closed-loop control result adjustment submodule excision number; Closed-loop control is with submodule rated voltage for input, and with submodule virtual voltage for feedback, output sub-module excises number adjustment amount.
8. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 7, is characterized in that, MMC submodule rated voltage U
smwith actual value u
smdeviation delta u
smbe ± Δ U through a threshold voltage
smhysteresis comparator, obtain excision number adjustment amount Δ m, by Δ m through an initial value be the controlled excision number m all pressing charging method to determine
ref, time constant is the integral controller of τ and rounds output, finally excised number; Described hysteresis comparator control logic is:
1) as Δ usm >=Δ Usm, Δ m=1;
2) as Δ usm≤-Δ Usm, Δ m=-1;
3) otherwise, Δ m is constant.
9. a kind of modular multi-level flexible direct-current transmission converter starting method according to claim 8, is characterized in that,
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