Model-Based Fault Diagnosis of 3-Phase CHB-nL Converters in Power Filter Applications

This paper introduces a model-based fault detection and isolation (FDI) strategy for an open-circuit fault (OCF) in the power switches of a 3-phase cascaded H-bridge (CHB) converter, in the generalized case of n-levels (CHB-nL). A 3-phase shunt active power filter (SAPF) application has been considered in this work. The proposed scheme consists of two stages: the first one is fault detection, which will be in charge of indicating which phase is faulty in the CHB-nL converter, and the second one is fault isolation. The fault detection stage is implemented by a sliding-mode observer in the α -ß -coordinates based on an additive modeling perspective of the faults. The isolation stage will identify the exact failing pair of switches within the H-bridge per phase. To achieve fault isolation, proportional-integral observers are proposed to estimate the DC fault profiles. Simulation results using a 3-phase 7-levels CHB (CHB-7L) converter with N=3 bridges are presented to assess the performance of the suggested FDI scheme. Our evaluation includes nominal conditions and a robustness test to step changes on the load side. © 2020 IEEE.

Bridge circuits; Electric fault currents; Power converters; Two term control systems; Cascaded H bridge (CHB); Model-based fault detection; Model-based fault diagnosis; Open circuit faults; Proportional integral observer; Robustness tests; Shunt active power filter (SAPF); Sliding mode observers; Fault detection

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