Asymmetrical operation of a twelve-pulse LCI drive system with power converter faults

This paper presents a study concerning the operation of a twelve-pulse LCI drive system after the occurrence of an open-switch fault in the line-side power converters. This type of fault introduces harmonics in the currents and in the electromagnetic torque, which normally don´t exist, degrading the operation of the drive. In order to improve the faulty operation, a compensated mode using an asymmetrical triggering of the semiconductors in the healthy converter is proposed. This results in a minimization or even elimination of some low order harmonics in the DC voltage and a smoothed DC link current and electromagnetic torque. Experimental results are presented to validate the proposed solution and compared with compensating schemes of the sequential triggering type. The main objective of this study is to introduce fault-tolerance and survivability characteristics to this high-power adjustable speed motor drive, therefore increasing its reliability and availability.