A Protection Method for Bridge Arm Short Circuit Fault of Modular Multilevel Converter

Abstract

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. It includes the following steps: 1) Setting the fault detection time interval Δt of the parallel protection switch of the bridge arm of the modular multilevel converter; 2) Setting the fault action threshold Q; 3) Setting the voltage thresholds Ulim.ac and Ulim.arm; 4) Detect the AC terminal-to-ground voltage Uac(t) of the modular multilevel converter, and calculate Q1=abs(aveage(Uac(Δt)))‑Ulim.ac; 5) Detect the bridge arm voltage of the modular converter Uarm(t), calculate Q2=abs(aveage(Uarm(Δt)))-Ulim.arm; 6) Judgment: If Q2×Q1>Q, then a bridge arm short-circuit fault occurs; 7) When judging the modular multi-level A bridge arm short-circuit fault occurs in the converter, which triggers the parallel protection switch of the sound phase bridge arm. The invention adopts the bridge arm parallel protection switch, which reduces the bridge arm short-circuit fault duration of the modular multilevel converter, reduces the DC bias voltage borne by the transformer and the overvoltage borne by the bridge arm of the converter, and reduces equipment requirements And cost, improved economy and safety.

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. 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 to the groun...

AI Technical Summary

Problems solved by technology

[0004] The main hazards of the short-circuit fault of the bridge arm of the modular multilevel converter include: 1) The output voltage waveform of the converter changes to a sinusoidal waveform with DC bias, causing the operating voltage of the bridge arm reactor or (and) 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 power electronic devices and capacitors to fail, or even explode

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