CN105633896B - A kind of DC voltage can continuously wide scope adjust direct current ice melting method - Google Patents
A kind of DC voltage can continuously wide scope adjust direct current ice melting method Download PDFInfo
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- CN105633896B CN105633896B CN201510027193.4A CN201510027193A CN105633896B CN 105633896 B CN105633896 B CN 105633896B CN 201510027193 A CN201510027193 A CN 201510027193A CN 105633896 B CN105633896 B CN 105633896B
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- 238000002844 melting Methods 0.000 title claims abstract description 14
- 230000008018 melting Effects 0.000 title claims abstract description 13
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- 239000003990 capacitor Substances 0.000 claims description 2
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Abstract
The present invention relates to a kind of DC voltage can continuously wide scope adjust direct current ice melting method.Existing DC de-icing device operation can consume certain idle, generation harmonics；Nearest level in MMC approaches modulation（NLM）Limited by submodule number, have 0≤n down,n up≤N, when ovennodulation occurs in modulating wave rise to a certain extent.The present invention utilizes bridge-type modularization multi-level converter (FBMMC) way traffic ability, is made of the full-bridge submodule of control flexibility ratio higher, applied to ice-melt, it is possessed the ability that direct current continuously adjusts.Core scheme of the present invention is：First, definition can be more than 1 modulation ratiom, the amplitude of modulating wave can be made very high；Secondly, calculate and put into equivalent conducting submodule number per moment upper and lower bridge arm；Finally, utilizeN 0Realize that MMC DC voltages continuously adjust, while ensure to exchange side waveform.Method proposed by the invention, can realize that DC voltage is continuously adjusted on a large scale, to adapt to different length line ice-melting, and can ensure to exchange quality.
Description
Technical Field
The invention belongs to the technical field of power transmission and distribution, and particularly relates to a direct-current ice melting method with a direct-current voltage capable of being adjusted continuously and widely.
Background
Among natural disasters encountered by various power systems, ice and snow disasters are one of the most serious. Compared with other accidents, the damage of the ice and snow disaster to the power grid is more serious under the general condition, the ice is flashed when the ice is light, the tower is broken when the ice is heavy, and even the power network is broken down.
In recent years, due to the frequent occurrence of ice disasters, dc ice melting devices have become conventional devices in power grids in ice-prone areas. The existing direct current ice melting device adopts a thyristor controllable rectification technology, consumes certain reactive power in operation, generates characteristic subharmonic waves and brings certain influence on access to an alternating current system.
The real-time expression of the number of submodules input by upper and lower bridge arms in recent level approximation modulation (NLM) in the existing MMC can be as follows:
（1）
（2）
（3）
whereinn down，n up，N，u S，U C，mRespectively represent: the number of the sub-modules input by the lower bridge arm, the number of the sub-modules input by the upper bridge arm, the number of the sub-modules input by a single bridge arm, a modulation wave, a direct current voltage average value of the sub-modules and a modulation ratio. However, the number of the sub-modules is limited to 0 ≦n down，n up≤NTherefore, after the modulation wave rises to a certain level, overmodulation may occur due to the number of levels limitation.
Disclosure of Invention
Aiming at the defects of the existing thyristor ice melting device and the overmodulation problem when the modulation wave of the existing MMC is too high in the background technology, in order to solve the problems, the full-bridge modular multilevel converter has the bidirectional operation capacity of direct-current voltage and direct-current, the requirement of direct-current ice melting on the operation condition of the converter can be met, each submodule of the full-bridge modular multilevel converter is composed of a full-bridge submodule with higher control flexibility, and the full-bridge modular multilevel converter is applied to direct-current ice melting and can overcome the defects.
The invention outputs positive, zero and negative module voltages according to a certain control and modulation rule, can enable the direct-current side voltage of the converter to be continuously adjustable between a rated value and zero, can melt ice for single lines with different lengths in a certain range, and is simple to operate. Meanwhile, when the converter outputs lower direct-current voltage and direct current, the converter can also be ensured to output higher-quality voltage and current on the alternating-current side, and when the number of the full-bridge submodules connected in series is higher, harmonic waves can not be fed into the alternating-current bus of the connected transformer substation.
The technical scheme of the invention is characterized by comprising the following steps:
step 1: defining a new modulation ratiomSo that the amplitude of the modulated wave can be very high, much greater than the amplitude of the DC voltage, i.e.mMay be much larger than 1.
Step 2: when the nearest level approximation modulation (NLM) is adopted, the original sub-module number invested by an upper bridge arm and a lower bridge arm at each moment is not used when the sub-module number invested by the upper bridge arm and the lower bridge arm at each moment is calculatedN(number of submodules per bridge arm) using the existing bridge armN 0(equivalent conducting submodule number).
And step 3: by usingN 0The MMC is introduced to realize large-range continuous adjustment of the direct-current voltage of the MMC, and meanwhile, the good waveform of an alternating-current side is guaranteed.
The invention can realize continuous large-range adjustment of direct current voltage through three steps so as to adapt to ice melting of lines with different lengths, ensure good quality of an alternating current side and have effectiveness and practicability.
Drawings
FIG. 1 shows the number of upper arms conducting when the present invention is applied to nearest level approximation modulationn upSet a DC voltageU dc=2kV，U c0=1kV, number of submodules per bridge armN=4, number of equivalent submodules to be switched onN 0=2, if the modulation is approached according to the existing recent level, the amplitude of the modulation wave is only 1 at maximum, but the invention utilizes the capability of the full-bridge sub-module to output a negative level, and the amplitude of the modulation wave can be 3 as shown in fig. 1. When in usen upWhen the ratio is not less than =2,n down=0, whenn upWhen the ratio is not less than =3,n down= -1, and so on, (4, -2), (3, -1), (2, 0), (1, 1), (0, 2), (-1, 3), (-2, 4), (-1, 3), (0, 2), (1, 1), (2, 0), respectively, which is one cycle period.
Using the number of equivalently conducting submodulesN 0The direct current voltage can be ensured to be constant at 2kV, but the amplitude of the alternating current voltage can be 3kV at the moment, and the number of levels is 7.
Modulation ratio when DC voltage drops to a lower levelmThe larger the amplitude of the modulated wave, the higher the ac voltage level. For example when the dc voltage is reduced from 2kV to 1kV,n upwill range from 4 to-3, while at the same timen downIt will be from-3 to 4,mwill reach 7 and the ac voltage amplitude will reach 7kV with a level number of 8.
Detailed Description
The following will describe in detail a dc ice melting method of the present invention in which dc voltage can be continuously adjusted in a wide range. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.
The technical problem to be solved by the invention is to pass through a full-bridge type modularized multi-level converter adopting full-bridge sub-modules and pass through the equivalent conduction numberN 0The invention adopts the following technical scheme to realize the continuous wide-range adjustment of the DC voltage of the converter:
the invention is realized by the following three steps:
step 1: defining a new modulation ratiomIs specifically shown as
（4）
Wherein,N 0indicating the number of equivalently conducting sub-modules (see step 2 in particular),mmay be much larger than 1 so that the amplitude of the modulated wave may be very high, much larger than the dc voltage amplitude.
Step 2: when the nearest level approximation modulation (NLM) is adopted, the original sub-module number invested by an upper bridge arm and a lower bridge arm at each moment is not used when the sub-module number invested by the upper bridge arm and the lower bridge arm at each moment is calculatedN(number of submodules per bridge arm) using the existing bridge armN 0：
（5）
（6）
Wherein:ceilingis a function of the rounding-up,U c0representing the sub-module capacitor voltage at nominal operation. In particular, since the present invention uses the full-bridge sub-module, the upper or lower bridge arm may output a negative voltage, so thatn upOrn downPossibly negative, e.g. upper arm output-5U c0Voltage at this timen upIt is-5.
And step 3: by usingN 0The introduction of the method realizes the continuous adjustment of the direct-current voltage of the MMC in a large range and is obtained by the nearest level approximation calculationn upAndn downis no longer in the range 0. ltoreq.n down，n up≤NBut the maximum range can be reachedN≤n down，n up≤N. And simultaneously, the good waveform of the alternating current side is ensured. The ice melting can be carried out on lines with different lengths within a certain range, and meanwhile, when the converter outputs lower direct-current voltage and direct current, the converter can also be ensured to output higher-quality voltage and current on the alternating-current side.
It should be noted that steps 1,2 and 3 are taken as the summary of the invention as a whole, and the three steps are organic, indivisible and integral.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (1)
1. A DC ice melting method with continuously and widely adjustable DC voltage is characterized in that the number of equivalent conduction sub-modules is introducedN 0The method comprises the following steps: step 1: defining a new modulation ratiomSo that the amplitude of the modulated wave can be very high, much greater than the amplitude of the DC voltage, i.e.mCan be much greater than 1, whereinmIs expressed as，NRepresenting the number of submodules of each bridge arm; step 2: miningCalculating the number of submodules invested by upper and lower bridge arms at each moment by using nearest level approximation modulation (NLM)N 0(number of equivalently conducting submodules), in whichN 0Is expressed asAnd isCeiling represents an rounding-up function,U dcwhich is representative of the direct voltage of the dc voltage,U c0represents the sub-module capacitor voltage at nominal operation,n upthe number of the sub-modules thrown into the upper bridge arm is shown,n downrepresenting the number of the lower bridge arm input sub-modules; and step 3: by usingN 0The MMC can continuously adjust the direct-current voltage in a large range, and simultaneously ensures that the alternating-current side has a sinusoidal step wave with higher electric energy quality, so that the requirements of lines with different lengths for deicing are met.
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| CN105914692A (en) * | 2016-06-17 | 2016-08-31 | 华北电力大学 | Full-bridge MMC direct-current ice melting device and control method thereof |
| CN112087156B (en) * | 2020-08-25 | 2021-12-10 | 东南大学 | Level approximation modulation method based on third harmonic injection |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102570369A (en) * | 2012-01-20 | 2012-07-11 | 南方电网科学研究院有限责任公司 | Design method of direct-current ice melting device without special converter transformer |
| CN102739080A (en) * | 2012-06-21 | 2012-10-17 | 北京四方继保自动化股份有限公司 | Direct current de-icing device based on full-bridge modular multilevel converter |
| CN103018583A (en) * | 2012-08-03 | 2013-04-03 | 中国能源建设集团广东省电力设计研究院 | Level number selecting and verifying method based on flexible direct-current transmission system of MMC (Modular Multilevel Converter) |
| CN204030512U (en) * | 2014-06-03 | 2014-12-17 | 南方电网科学研究院有限责任公司 | Voltage source type direct-current ice melting and static synchronous compensation device |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102570369A (en) * | 2012-01-20 | 2012-07-11 | 南方电网科学研究院有限责任公司 | Design method of direct-current ice melting device without special converter transformer |
| CN102739080A (en) * | 2012-06-21 | 2012-10-17 | 北京四方继保自动化股份有限公司 | Direct current de-icing device based on full-bridge modular multilevel converter |
| CN103018583A (en) * | 2012-08-03 | 2013-04-03 | 中国能源建设集团广东省电力设计研究院 | Level number selecting and verifying method based on flexible direct-current transmission system of MMC (Modular Multilevel Converter) |
| CN204030512U (en) * | 2014-06-03 | 2014-12-17 | 南方电网科学研究院有限责任公司 | Voltage source type direct-current ice melting and static synchronous compensation device |
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