An Open Circuit Fault-Tolerant Method for Cascaded Cross-Switched Multilevel Inverter

This paper proposes a novel switch open-circuit (O.C.) fault detection and fault-tolerant method for cascaded cross-switched inverters (CCSIs). Although CCSIs offer the advantage of achieving the same voltage levels with fewer power devices compared to alternative cascaded modular multilevel converters, ensuring safe operation under fault conditions remains a challenge. In the proposed method, for fault detection, the actual and expected AC-side voltage waveforms of the inverter are compared, and a set of error indices is defined through which the failed switch is identified in less than a fundamental cycle. Afterward, to provide fault tolerance, an auxiliary cell (AUC) with capacitive DC-links is added to the circuit without the need for backup DC sources. A variable-clamp-level modulation method is proposed to modify the reference voltage of the inverter phases. The suggested method facilitates the charging of capacitors in the transient mode and maintains the balance of capacitor voltages in a steady-state post-fault situation. The several simulation and experimental results on a 9-level CCSI indicate that the inverter successfully continues operation after failure, confirming the above claims.