MMC sub-module IGBT open-circuit fault diagnosis method based on current error

Abstract

The invention discloses an MMC sub-module IGBT open-circuit fault diagnosis method based on a current error, and the method comprises the steps: carrying out the fault positioning based on a fault type and a bridge arm current direction according to an error between a sub-module capacitor current prediction value and a capacitor current actual value, and a fault state of a corresponding sub-module as a fault feature; and according to the capacitance current error fault information of each sub-module and mutual independence of the fault information of each sub-module when different types of faults and different sub-module faults occur, fault positioning of the plurality of sub-modules is carried out. According to the method, the capacitance current error fault information of each sub-module is directly utilized during sub-module IGBT open-circuit fault detection, and the fault information of each sub-module is mutually independent when different types of faults and different sub-module faults occur, so that the fault positioning of a plurality of sub-modules can be realized, the accuracy of fault positioning is improved, and the fault positioning efficiency is improved. And the LS-SVM dichotomy network is used to carry out rapid positioning of sub-module faults.

Description

technical field [0001] The invention relates to the field of electric power technology, in particular to a method for diagnosing an open circuit fault of an MMC sub-module IGBT based on a current error. Background technique [0002] With the widespread consumption of distributed power sources, the rapid growth of large-scale loads of electric vehicles and diversified access, the structure and operation of the existing distribution network are also changing. How to ensure the economical transmission, distribution and efficient use of renewable energy in the existing distribution network and to accommodate diversified needs has become an important goal of future smart grid development. [0003] In view of the deficiencies that most of the existing primary power distribution equipment are limited by capacity, adjustment times and continuity, scholars at home and abroad have proposed the concept of flexible interconnection equipment (FID). The distribution network is flexibly i...

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Problems solved by technology

[0005] For the IGBT open-circuit fault location of the FID sub-module composed of MMC, a lot of related research has been done at home and abroad. Some scholars have proposed an open-circuit fault location method that can accurately locate the faulty sub-module. However, the proposed method is only applicable to a single sub-module fault. , cannot accurately locate faults when multiple IGBT open-circuit faults occur, and has certain engineering applicability. For MMC systems, multi-tube faults have a greater impact on the output of sub-modules and systems, seriously affecting the safe and stable operation of MMC. Some scholars have proposed Accurate positioning of single and multiple IGBT open-circuit faults is realized based on the characteristics of the fault capacitor, but the fault capacitor voltage needs to be within a certain period of time and is related to the operating conditions and fault types of the system, the fault location time is long, and the threshold selection is difficult

[0006] In order to further reduce the fault diagnosis time and reduce the calculation speed of the controller, some scholars have proposed to change the location and number of sensors connected, measure the output voltage or add bridge arm inductance voltage sensors instead of measuring the sub-module capacitor voltage, however, it is necessary to change The existing MMC system structure will also bring certain potential risks to the system; on the basis of not adding sensors, some scholars propose to adopt an improved RSF sorting balance algorithm, and propose a virtual capacitor voltage for the switching of SMs in the fault group. Further speed up the switching speed, but in the case of a large number of neutron modules in the bridge arm, switching takes a long time, and even the current of the bridge arm changes direction during the switching process, which eventually leads to the problem that the open circuit fault cannot be located

[0007] In general, the current sub-module IGBT open-circuit fault location method cannot quickly diagnose multiple sub-module IGBT open-circuit faults. The fault location method fails to make full use of the information of the faulty sub-module itself, and the fault location process and threshold selection are complicated. Based on this, A current error-based MMC sub-module IGBT open-circuit fault diagnosis method is proposed to solve the above problems

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