Modular multilevel converter bridge arm short circuit fault protection method

Abstract

The invention relates to fault protection methods of converters, specifically to a modular multilevel converter bridge arm short circuit fault protection method. The method comprises the following steps of 1) setting a fault detection time gap [delta]t of modular multilevel converter bridge arm parallel protection switches; 2) setting a fault motion threshold value Q; 3) setting voltage threshold values Ulim.ac and Ulim.arm; 4) detecting voltage to ground Uac(t) of the alternating-current end of a modular multilevel converter and computing Q1=abs(aveage(Uac([delta]t)))-Ulim.ac; 5) detecting bridge arm voltage Uarm(t) of the modular multilevel converter and computing Q2= abs(aveage(Uarm([delta]t)))-Ulim.arm; 6) determining that a bridge arm short circuit fault occurs if Q2 x Q 1 > Q; and 7) trigging the bridge arm parallel protection switch of a sound phase when it is determined that the modular multilevel converter has the bridge arm short circuit fault. According to the invention, by employing the bridge arm parallel protection switches, the bridge arm short circuit fault time duration of the modular multilevel converter is shortened; the direct-current bias voltage borne by a transformer and the overvoltage borne by converter bridge arms are reduced; the equipment requirement and cost are lowered; and the economical efficiency and security are improved.

Description

technical field [0001] The invention relates to a fault protection method for a converter, in particular to a protection method for a bridge arm short-circuit fault of a modular multilevel converter. Background technique [0002] Modular Multilevel Converter (MMC) is a converter based on turn-off devices and pulse width modulation technology. Currently, the most commonly used turn-off devices are insulated gate bipolar Transistors (IGBTs). Compared with the traditional line voltage commutated converter (Line Commutated Converter, LCC), the modular multilevel converter uses a large number of energy storage capacitors, and at the same time makes the output voltage of the converter during operation The waveform remains the same. Therefore, from the perspective of grid operation voltage stability and voltage AC harmonic reduction, the modular multilevel converter has obvious advantages. [0003] During normal operation, the output voltage of the modular multilevel converter t...

AI Technical Summary

Problems solved by technology

[0004] The main hazards of bridge arm short-circuit faults in modular multilevel converters include: 1) The output voltage waveform of the converter changes to a sinusoidal waveform with DC bias, causing the bridge arm reactor or (and) the operating voltage of the transformer to appear DC bias, equipment noise and loss increase; 2) Make the non-faulty bridge arm connected to the same AC terminal withstand power frequency overvoltage, which may cause failure of power electronic devices and capacitors, and even explosion

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