CN103532418A - SVG submodule capacitor pre-charging strategy based on MMC - Google Patents
SVG submodule capacitor pre-charging strategy based on MMC Download PDFInfo
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- CN103532418A CN103532418A CN201310137253.9A CN201310137253A CN103532418A CN 103532418 A CN103532418 A CN 103532418A CN 201310137253 A CN201310137253 A CN 201310137253A CN 103532418 A CN103532418 A CN 103532418A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/36—Means for starting or stopping converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
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Abstract
The cumbersome, complex structure and other problems for current multi-level converter power cell capacitor pre-charge method process, the present invention relates to a kind of novel SVG (Static Var Generator) power cell capacitor precharge artifacts based on MMC (Modular Multilevel Converter). This method only needs additionally to increase by one group of current-limiting resistance R and one group of resistance excision switch S on hardware configuration, and current-limiting resistance is serially connected between inverter and AC network, and hardware configuration is succinct. Precharge artifacts use voltage, current double closed-loop control mode, submodule voltage after system starting
It is tracked by Voltage loop and electric current loop two close cycles to constant current
Active power is absorbed from power grid, so that inverter works in invariable power boost mode in the charging stage, charge smooth trajectory. After charging complete, Voltage loop adjuster moves back saturation, while cutting off current-limiting resistance, and system enters normal mode of operation. The strategy completes the precharge of power cell, and charge rate is controllable under the premise of no increase additional hardware circuit and control algolithm.
Description
Technical field
Patent of the present invention relates to a kind of flying capacitor pre-charge system and method, is specifically related to a kind of SVG power cell electric capacity precharge strategy based on MMC.
Background technology
Rapidly, the power conversion technology of many level arises at the historic moment the development of recent year power industry.High-voltage large-capacity converter starts or restarts and in process, is generally accompanied by great transient state energy and impacts, and its power switch component need to bear great current temporary state stress.
Modular multilevel inverter (Modular Multilevel Converter, MMC) be in high-power transmission etc., need to export from common DC bus to AC a kind of multilevel converter topological structure that the inversion occasion of energy receives much concern in recent years, it adopts the mode of a plurality of submodule cascades to realize the object of high-power, by controlling input and the excision of each submodule, can make the output waveform of converter approach sine wave, there is good harmonic characterisitic.
As shown in Figure 1, three-phase MMC is comprised of three brachium pontis MMC topological structure, and each brachium pontis is in series by N submodule and a reactor L, and each brachium pontis is directly connected with common DC bus.This rating of set module is many, during startup, for guaranteeing that each submodule capacitance voltage can arrive rapidly rated voltage and need to carry out precharge to MMC.
At " Proceedings of the CSEE, 2009, 29(30), 1～6 page " " novel modularized many level VSC submodule capacitance parameter with all press strategy " of publication proposed a kind of " by module charging " pre-charge method specific implementation method of additional auxiliary DC power supply that adopts and be: choose the outside direct voltage source that approximates greatly submodule rated voltage, be connected across the bus both sides of MMC, send cut-off signals first to the S1 of 2N submodule of each phase, except submodule to be charged, open signal to the S2 transmission of all the other 2N-1 submodule, when this submodule capacitance voltage equals rated voltage by the time, its charging is complete, open signal now to the S2 transmission of this submodule, send cut-off signals to the S1 of next submodule to be charged, start the pre-charge process of next submodule, the like, after 2N precharge, MMC precharge completes.It is low that its advantage is that the transient state in pre-charge process is processed energy grade, is applicable to the limited occasions of available DC power supply such as laboratory.Weak point is when MMC power cell quantity is more, the method easily causes first charging and rear charge power unit DC capacitor voltage to have deviation, when serious, the output characteristic of MMC will be affected, due to extra auxiliary DC power supply of needs, in engineering application, can increase system hardware complexity simultaneously.
Publication number: CN102170140A patent disclosed " a kind of starting method of modularization multi-level converter flexible DC power transmission system " has proposed a kind of MMC starting method for flexible DC power transmission, first the method passes through current-limiting resistance, employing is not controlled rectification electric capacity is charged, after capacitance voltage is stable, unlock switch pipe, bypass current-limiting resistance, system directly drops into capacitance voltage closed-loop control.Detailed process is divided into three phases: the first stage, first all switching tubes of locking, open current-limiting resistance by-pass switch, two current conversion station MMC submodule electric capacity are not controlled to rectification charging, after capacitance voltage is stable, enter second stage, the switching signal of release current conversion station MMC2, and make it enter capacitance voltage closed-loop control, after MMC2 submodule capacitance voltage is stable, enter the phase III, closed current-limiting resistance by-pass switch, the switching signal of release current conversion station MMCl, and make it enter capacitance voltage closed-loop control, after two current conversion station submodule capacitance voltages are stable, charging finishes.But the method still needs continuous Detection capacitance magnitude of voltage, and when the phase III starts, all submodule capacitance voltage sums of every phase brachium pontis equal AC voltage peak, the rated voltage U while being less than MMC normal operation
dc, bypassing after current-limiting resistance, system is directly carried out the control of closed loop capacitance voltage can cause very large impulse current, produces potential safety hazard.
" without the method for starting three-phase modular multilevel inverter of auxiliary DC power supply " (patent publication No.: CN101795057A) of the people such as Xu Zheng, Tu Qingrui, proposed in a kind of situation without auxiliary DC power supply, the self-excitation charging method of three-phase modular multilevel inverter, the method utilizes AC power to replace DC power supply, the on off state of controlling submodule by detecting brachium pontis current polarity and submodule capacitance voltage, completes the charging of the submodule of converter.Specific implementation process is: by current-limiting resistance, AC power and converter are connected, give switching device S1 cut-off signals on all submodules, open signal to switching device S2 under all submodules, detect the electric current of each brachium pontis, when electric current is consistent with charging direction, give switching device S2 cut-off signals under submodule to be charged, this submodule charging.When electric current and charging opposite direction, keep under this submodule switching device in off state, this submodule capacitance voltage is kept, so repeatedly, and when submodule capacitance voltage reaches specified, open switching device S2 under this submodule, the charging of this submodule is complete, can continue next submodule to charge, and repeats above-mentioned steps, until all submodule capacitance voltages of brachium pontis all reach rated value, converter submodule electric capacity completes charging.But the method is in each brachium pontis charging process of converter, and only individual module drops into charging at every turn, and the charging interval of converter increases doubly, and in capacitor charging process, needs Detection capacitance magnitude of voltage and the brachium pontis sense of current, controls more complicated.
Therefore introduce rational precharge strategy and there is very major and immediate significance for promoting MMC technology.
Summary of the invention
The problem existing for above pre-charge method, the present invention proposes a kind of novel SVG brachium pontis submodule electric capacity precharge strategy based on MMC.
This precharge model structure is simple, has only increased a current limliting module I on hardware, and current limliting module I comprises charging current limiter resistance R and resistance excision switch S, and this current limliting module I one end is connected with inverter output end, and the other end is connected with grid side voltage.Its control circuit adopts electric current loop II and the two closed-loop controls of Voltage loop III, after system starts, reaches the amplitude limit value of pi regulator output.By PR adjuster control inverter output current tracing preset electric current, make inverter absorb active power from electrical network, after having charged, pi regulator moves back saturated, excises current-limiting resistance simultaneously, and system starts normal operation.
Compared with prior art, advantage of the present invention is:
1) this novel whole process of SVG submodule electric capacity precharge strategy based on MMC, completes automatically by Voltage loop III, electric current loop II, can realize by the natural transition that is pre-charged to steady operation.
2) this novel SVG submodule electric capacity precharge strategy based on MMC can be realized a plurality of submodules are charged simultaneously, charging smooth trajectory.
3) this novel SVG submodule electric capacity precharge strategy based on MMC can regulate the speed of precharge easily by the output violent change of the outer ring controller of regulation voltage, has higher flexibility.
4) this novel SVG submodule electric capacity precharge strategy based on MMC only need convert at normal compensation policy end, without increasing extra control algolithm.
Accompanying drawing explanation
Fig. 1 is the SVG major loop based on MMC.
The SVG precharge theory diagram of Fig. 2 based on MMC.
Fig. 3 submodule average voltage and each phase submodule average voltage charging track
The single-phase submodule capacitance voltage charging of Fig. 4 track
In figure: the I flow module that is limited; II is electric current loop; III is Voltage loop; IV is submodule capacitance voltage control module.
Embodiment
Below in conjunction with Fig. 1 and Fig. 2, brachium pontis electric capacity precharge strategy and the operation principle thereof based on many level MMC of the present invention is described further.As shown in Figure 1, the brachium pontis electric capacity precharge policy construction model based on many level MMC of the present invention only increases charging current limiter resistance and resistance excision switch at former interchange outlet side, simple in structure.Its control principle as shown in Figure 2, in figure
for all submodule average voltages in MMC,
for the given voltage of submodule, V
dcxfor all submodule capacitance voltage actual values, △ V
dcpfor alternate energy is controlled output three-phase controlled quentity controlled variable, △ V
dcxfor each submodule capacitance voltage controlled quentity controlled variable, PI is Voltage loop adjuster, and PR is electric current loop adjuster,
for meritorious electricity in the computing of FBD current detecting is led,
for idle electricity is led,
for electric current loop is given, i
ffor SVG compensation output current.
System starts initial time
dC bus-bar voltage controller PI is saturated very soon, △ G
preach the amplitude limit value of PI output, △ G
pbe superimposed to the meritorious axle in FBD current detecting link, current loop control inverter output current tracing preset electric current
inverter absorbs active power from electrical network, total energy storage of each power cell increases, and the energy even that inverter inside is controlled by alternate energy and the control of submodule capacitance voltage absorbs inverter is assigned in the middle of each power cell, each submodule capacitance voltage raises gradually, when
time, pi regulator surrender and, system normal operation, whole precharge link completes automatically, and without extra program or equipment.
Precharge zero hour, before the output line voltage of inverter is less than power line voltage, SVG cannot inject reactive power compensation electric current to electrical network, for guaranteeing the smooth of charging curve, can, in pre-charging stage, make in Fig. 2
be inverter only with the gain merit exchange of energy of electrical network, and the amplitude limit value size that the amplitude of energy exchange can be exported by PI controls, when DC bus-bar voltage surpasses set-point, DC bus-bar voltage controller moves back saturated, now restoring current detection
axle, system is switched to compensation model, and precharge link finishes.The outlet side series limiting resistor of inverter, the impulse current of restriction inverter when output voltage is lower, when precharge finishes, by closed S switch excision current-limiting resistance, system enters normal mode of operation.
In above-mentioned pre-charge process, need predetermined hardware device only to have pre-charge resistance, its resistance can allow the maximum current flowing into choose by inverter, according to above-mentioned analysis, maximum current appears at precharge initial time, now inverter output voltage is zero, system is equivalent to short circuit, and therefore, if determine, maximum permissible current can show that the approximate formula of pre-charge resistance is
U in formula
sfor the effective value of AC power phase voltage, I
pcmfor allowing to flow into the maximum current of inverter in pre-charge process.
Fig. 3 has provided modular multilevel converter three-phase submodule average voltage of the present invention and each phase submodule average voltage charging track.
Fig. 4 has provided the single-phase submodule capacitance voltage charging of modular multilevel converter of the present invention track.
By obtaining the analysis of this submodule electric capacity precharge strategy, whole charging process completes automatically by Voltage loop, electric current loop, and by precharge, is finished to normal operation transition nature capacitance voltage charging smooth trajectory.
Claims (3)
1. the novel SVG submodule electric capacity precharge strategy based on MMC, it is characterized in that: this precharge model structure is simple, on hardware, only increased a current limliting module I, current limliting module I comprises charging current limiter resistance R and resistance excision switch S, current limliting module is serially connected with between inverter output and AC network, adopt electric current loop II and Voltage loop III double circle controling mode, by the total energy storage of Voltage loop control inverter DC side, obey given, regulate inverter and AC to exchange meritorious size and Orientation, and the meritorious upper limit is determined by the output violent change of Voltage loop pi regulator, output current by current loop control inverter is obeyed given.
2. the novel SVG submodule electric capacity precharge strategy based on MMC of narrating according to claim 1, is characterized in that: in pre-charge process, Voltage loop pi regulator is saturated, is output as amplitude limit value Δ G
p, by Δ G
pbe superimposed to the meritorious axle in FBD current detecting link, testing result is given as electric current loop, by two closed loop co-controlling SVG, works in the permanent power charging stage.
3. the novel SVG submodule electric capacity precharge strategy based on MMC of narrating according to claim 1, is characterized in that: inverter inside is controlled with power cell capacitance voltage control IV and combined each power cell that is assigned to of the energy even of inverter absorption by alternate energy.
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Cited By (8)
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|---|---|---|---|---|
| CN104993686A (en) * | 2015-07-22 | 2015-10-21 | 华中科技大学 | Method for starting single-phase rectifier based on modular multilevel converter |
| CN107925362A (en) * | 2015-08-03 | 2018-04-17 | 超级电力研究所有限公司 | Simulated capacitance |
| CN110336478A (en) * | 2019-07-08 | 2019-10-15 | 国电南瑞科技股份有限公司 | A kind of inactive side power cell pre-charge method of back-to-back semi-bridge type MMC circuit |
| CN110471469A (en) * | 2019-09-26 | 2019-11-19 | 湖南航天机电设备与特种材料研究所 | A kind of adaptive temperature control method based on PI algorithm |
| CN112134296A (en) * | 2020-09-16 | 2020-12-25 | 西安爱科赛博电气股份有限公司 | Three-level static var generator with auxiliary voltage sharing and voltage sharing method thereof |
| CN114301036A (en) * | 2021-12-28 | 2022-04-08 | 南瑞集团有限公司 | Cascade multilevel converter and on-load and no-load starting method thereof |
| CN117650692A (en) * | 2023-11-16 | 2024-03-05 | 燕山大学 | Energy storage converter overcurrent inhibition method |
| CN117792063A (en) * | 2024-02-23 | 2024-03-29 | 四川大学 | Hybrid modular multilevel converter AC/DC side precharge starting control strategy |
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Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104993686B (en) * | 2015-07-22 | 2017-06-30 | 华中科技大学 | A kind of single-phase rectifier based on Modular multilevel converter starts method |
| CN104993686A (en) * | 2015-07-22 | 2015-10-21 | 华中科技大学 | Method for starting single-phase rectifier based on modular multilevel converter |
| CN107925362B (en) * | 2015-08-03 | 2021-01-12 | 超级电力研究所有限公司 | Virtual capacitor |
| CN107925362A (en) * | 2015-08-03 | 2018-04-17 | 超级电力研究所有限公司 | Simulated capacitance |
| CN110336478A (en) * | 2019-07-08 | 2019-10-15 | 国电南瑞科技股份有限公司 | A kind of inactive side power cell pre-charge method of back-to-back semi-bridge type MMC circuit |
| CN110336478B (en) * | 2019-07-08 | 2021-01-26 | 国电南瑞科技股份有限公司 | Passive side power unit pre-charging method of back-to-back half-bridge type MMC circuit |
| CN110471469B (en) * | 2019-09-26 | 2021-03-16 | 湖南航天机电设备与特种材料研究所 | Self-adaptive temperature control method based on PI algorithm |
| CN110471469A (en) * | 2019-09-26 | 2019-11-19 | 湖南航天机电设备与特种材料研究所 | A kind of adaptive temperature control method based on PI algorithm |
| CN112134296A (en) * | 2020-09-16 | 2020-12-25 | 西安爱科赛博电气股份有限公司 | Three-level static var generator with auxiliary voltage sharing and voltage sharing method thereof |
| CN112134296B (en) * | 2020-09-16 | 2022-03-11 | 西安爱科赛博电气股份有限公司 | Three-level static var generator with auxiliary voltage sharing and voltage sharing method thereof |
| CN114301036A (en) * | 2021-12-28 | 2022-04-08 | 南瑞集团有限公司 | Cascade multilevel converter and on-load and no-load starting method thereof |
| CN114301036B (en) * | 2021-12-28 | 2024-03-26 | 南瑞集团有限公司 | Cascaded multi-level converter and on-load and off-load starting method thereof |
| CN117650692A (en) * | 2023-11-16 | 2024-03-05 | 燕山大学 | Energy storage converter overcurrent inhibition method |
| CN117650692B (en) * | 2023-11-16 | 2024-05-17 | 燕山大学 | Energy storage converter overcurrent inhibition method |
| CN117792063A (en) * | 2024-02-23 | 2024-03-29 | 四川大学 | Hybrid modular multilevel converter AC/DC side precharge starting control strategy |
| CN117792063B (en) * | 2024-02-23 | 2024-05-10 | 四川大学 | Hybrid modular multilevel converter AC/DC side precharge starting control strategy |
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Application publication date: 20140122 |