Extended Model of Chopper Cells for Open Circuit Fault Detection in Modular Multilevel Cascade Converters using Sliding Mode Observers

Fault detection and isolation (FDI) strategies can be implemented to increase reliability and prevent faults of power switches from disrupting converter operation. This is especially important for Modular Multilevel Cascade Converters (MMCC) due to the high number of switches employed in this topology. This paper proposes a new model for chopper cells, the core component of an MMCC. Unlike reported methods, the proposed model enables open-circuit fault detection and excellent tracking of cluster currents using a Sliding Mode Observer (SMO) under normal and faulty operation. The model has been successfully validated to detect faulty operation by using PLECS simulations in a BTB MMCC-DSCC.