Fault diagnosis and neutral point voltage control when the 3-level inverter faults occur

Many multi-level inverter faults have detected using the over voltage and the over current in their systems. However, the fault detection of the switching elements is very difficult because the voltage and current according to each switching fault decrease more then the normal operation. The dc-link unbalancing voltage when the 3-level inverter faults occur causes a serious problem in safety and reliability of system. Therefore, this paper proposes the simple fault diagnose method and the neutral-point voltage control method that can protect a system from the unbalancing voltage of the dc-link capacitors when the of switching element faults in the 3-level inverter occur that is very efficient in ac motor drives of the high voltage and high power applications. Through experimental results, the superiority of the proposed method is demonstrated.