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This paper proposes a simple modulation approach for symmetrical and asymmetrical cascaded multilevel converters, suitable for operation under normal and fault conditions. Initially, the set of all possible converter common-mode voltages for linear operation is derived, considering the status of each converter cell. It is demonstrated that the methods previously described in the literature belong to the derived set. By properly selecting the common-mode voltage, the entire converter voltage synthesis capability can be achieved under any fault condition. The proposed modulation approach has been applied for both symmetrical and asymmetrical cascaded multilevel converters. Simulation and experimental results show the effectiveness of the proposed modulation approach and validate the theoretical analysis.