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Fault tolerant controller for a generalized n-level CHB multilevel converter

This paper presents a model-based fault tolerant control strategy for open-circuit faults (OCFs) in the switching devices of a cascade H-bridge converter with n-levels (CHB-nL). In this study, we address the application of the CHB-nL converter as a single-phase active filter. The OCFs are modeled as additive signals into the subsystems describing the dynamics of each H-bridge in the converter. For diagnosis purposes, a bank of nonlinear proportional-integral (PI) observers are suggested to estimate the OCF profiles, independently of the operating point of the converter. Based on the estimated components, fault detection, isolation and reconfiguration is achieved. Furthermore, no additional sensors are needed to carry out the diagnosis media besides the ones used for control purposes. To validate the ideas proposed in this work, an experimental evaluation is carried out for a single OCF condition. The experimental results are used to confirm that the current tracking, voltage regulation and balance objectives can be obtained despite of OCFs in the active filter and highly distorted load currents.