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A pre-charge control method for inverters in a back-to-back mmc structure

A control method and inverter technology, which are used in electrical components, output power conversion devices, and AC power input conversion to AC power output, etc., can solve the problem of less research on pre-charging control strategies for MMC inverters.

Active Publication Date: 2020-04-10
LANZHOU UNIVERSITY OF TECHNOLOGY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Back-to-back MMC is composed of MMC rectifier and MMC inverter. There have been many public literatures that have introduced the pre-charging control method of MMC rectifier through the AC side in detail, but there are relatively few studies on the pre-charging control strategy of MMC inverter.

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  • A pre-charge control method for inverters in a back-to-back mmc structure
  • A pre-charge control method for inverters in a back-to-back mmc structure
  • A pre-charge control method for inverters in a back-to-back mmc structure

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Embodiment Construction

[0052] Such as figure 1 As shown, the inverter in the back-to-back MMC structure of the present invention is composed of three phase units, each phase is composed of upper and lower bridge arms, and each bridge arm is composed of n SMs (submodules) and a bridge arm inductance L It is formed in series, and the capacitance value of the sub-module is C. When back-to-back MMCs run stably, the DC bus voltage is U dc , sub-module capacitor voltage U C =U dc / n. The MMC rectifier is equivalent to a controllable current source, and the output current is I d .

[0053] The present invention is a kind of precharge control method of the inverter in back-to-back MMC structure, and its steps are: the precharge method of MMC inverter sub-module is divided into two stages, such as figure 2 As shown, in the first charging stage, the capacitors of all sub-modules of the MMC inverter are charged. In the second charging stage, first charge the n sub-modules put in, and cut off the remain...

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Abstract

A pre-charging control method for an inverter in a back-to-back MMC structure. Firstly, the first charging stage is performed, the charging current is controlled to charge the capacitors of all sub-modules of the MMC inverter, and the time for the charging current to act is calculated. Then proceed to the second charging stage. According to the end time of the first charging stage, the IGBT is controlled to be turned off and on, to charge the capacitor of the sub-module that is put in first, and to remove the remaining sub-modules. Finally, the on-off of the IGBT is controlled at the end of the capacitive charging of the sub-module that is first put into charging, and the sub-module that is first put into charging is cut off while the remaining sub-modules are being put in, and the entire pre-charging time can be calculated. In this way, the MMC inverter can be pre-charged by controlling the charging current, and the charging time can be minimized while ensuring safe charging. The charging state of the sub-module is controlled by the time node, and the sub-module capacitor voltage detection device is saved.

Description

technical field [0001] The invention relates to the technical field of MMC (modular multilevel converter), in particular to a precharge control method for an inverter in a back-to-back MMC structure. Background technique [0002] Compared with traditional multilevel converters, MMC has the characteristics of small switching loss, high output waveform quality, strong fault handling ability, easy expansion, and four-quadrant operation. The MMC system contains a large number of suspended sub-module capacitors, and all sub-module capacitors have no voltage before starting. When starting the MMC, it is first necessary to adopt a corresponding control method to charge the sub-module capacitor, and charge the sub-module capacitor to the voltage requirement for stable operation. The back-to-back MMC consists of MMC rectifiers and MMC inverters. There have been many published literatures that have introduced the pre-charging control methods for MMC rectifiers through the AC side in ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02M7/483H02M5/458
CPCH02M5/4585H02M7/483H02M7/4835
Inventor 王兴贵齐刚马平王海亮杨维满李晓英郭群郭永吉
Owner LANZHOU UNIVERSITY OF TECHNOLOGY