MMC half-bridge sub-module switch tube open-circuit fault identification and positioning method

Abstract

The invention relates to an MMC half-bridge sub-module switching tube open-circuit fault identification and positioning method, and belongs to the technical field of power electronic converter fault diagnosis. The method comprises the following steps: firstly, calculating a bridge arm current harmonic distortion rate, and when THD exceeds a threshold value, determining that a half-bridge sub-module switching tube of the bridge arm has an open-circuit fault; based on a capacitor voltage value of a half-bridge sub-module of a fault bridge arm, firstly, a proper decomposition signal is obtained through wavelet decomposition, a proper detail decomposition signal is selected to carry out Hilbert transform to obtain an envelope spectrum, effective fault features are extracted, and fault module detection is carried out through an outlier detection algorithm. According to the method, fault features can be effectively extracted, module fault diagnosis can be realized, and the fault sub-module can be accurately found in the bridge arm. And extra hardware resources are not needed. According to the method, fault diagnosis is completed based on data analysis and does not depend on an MMC analytical model, and the method is insensitive to uncertainty of system parameters and has high robustness.

Description

technical field [0001] The invention relates to a method for identifying and locating an open circuit fault of a switch tube of an MMC half-bridge sub-module, and belongs to the technical field of fault diagnosis of power electronic converters. Background technique [0002] Modular Multilevel Converter (MMC), referred to as MMC. Since its inception in 2002, it has increasingly become the most promising converter in the High Voltage Direct Current (HVDC) power transmission system due to its high modularity, good output waveform quality, low step voltage, and low device switching frequency. One of the streamer topologies. The above advantages of MMC come from the cascaded structure of its sub-modules. However, a large number of cascaded sub-modules contained in MMC also constitute a large number of potential failure points, which brings great challenges to the operational reliability of MMC. The sub-modules used by MMC are usually composed of switching elements and passive e...

AI Technical Summary

Problems solved by technology

Existing fault diagnosis methods for MMC mainly include methods based on hardware monitoring and location and methods based on model monitoring and location; however, the existing MMC model is only applicable to MMC under normal working conditions, and when an open circuit fault occurs in the MMC The MMC mathematical model is no longer applicable; at the same time, through the analysis of the sub-module in the switch tube T 1 or T 2 The current path characteristics of the open circuit can be known, the sub-module at T 1 or T 2 In the case of an open circuit fault, there are three states that are exactly the same as the sub-module operating states under normal conditions. Therefore, these three states cannot be diagnosed under the existing fault diagnosis method, which increases the diagnosis time of the fault diagnosis algorithm.

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