System and method for grouping and pre-charging modular multilevel converter capacitor

Abstract

The invention relates to a system for grouping and pre-charging modular a multilevel converter capacitor. The system comprises at least one modular multilevel converter MMC; an alternating-current side input end of the modular multilevel converter MMC is connected with a series-connected starting current-limiting resistor Rx, a breaker RBK1 (Remote Breaker) and an alternating-current power supply in turn; or the system comprises two modular multilevel converters MMCs which respectively are a first modular multilevel converter MMC1 and a second modular multilevel converter MMC2. A method for grouping and pre-charging the modular multilevel converter capacitor comprises the following steps of: respectively dividing half-bridge sub-modules of two modular multilevel converters MMCs into two groups and four groups, and carrying out grouping and pre-charging. According to the method for grouping and pre-charging the modular multilevel converter capacitor, the pre-charging of a capacitor is shortened, and the power consumption of the current-limiting resistor is reduced; the charging current direction is unnecessary to be detected, and the capacitor voltage closed-loop control is unnecessary as well; and the implementation is simple, and the control is simple.

Description

technical field [0001] The invention relates to a capacitor group precharging system and method, in particular to a modular multilevel converter capacitor group precharging system and method. Background technique [0002] Modular Multilevel Converter (MMC) topology adopts cascaded and modular structure, and can obtain multi-level ladder voltage without direct series connection of power devices, with lower dU / dt and lower Voltage harmonic content has broad application prospects in medium / high voltage large capacity systems (such as flexible direct current transmission). In application, the system usually consists of two three-phase MMC devices, the converter topology is as follows figure 1 As shown in the figure, the upper bridge arm and the lower bridge arm of each phase are formed by cascading N sub-modules (Sub-modular, SM), each sub-module SM is a half-bridge structure, as shown in Figure 2, the sub-module DC side with the same capacitor C in parallel. [0003] When th...

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Problems solved by technology

Although in the first and second stages of this method, due to the presence of current limiting resistors, the current impact is not large, but at the beginning of the third stage, because the capacitor voltage is still near the lower critical voltage (all sub-voltages of each bridge arm The sum of the module capacitor voltage is equal to the peak value of the AC side voltage), but after the current limiting resistor is bypassed, the system is directly put into the closed-loop control of the capacitor voltage, which will still generate a large inrush current in practice

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