Assessment of a Nine-Phase Induction Motor Drive for Metal Industry Applications

Metal industries combine several conditions that match with the advantages of multiphase motor drives, such as high power and high reliability. High power usually means cumbersome multilevel converters, with very expensive high-blocking voltage semiconductors. By adding more phases, it is possible to reduce the motor drive voltage levels and to use two-level converters with more common and less expensive low-blocking voltage power modules. High reliability means lower probability of unexpected production interruption, which is achieved by the fault-tolerant characteristic of the multiphase motor drive. In this article, a wire rod plant is depicted and the replacement of a traditional three-phase motor drive by a nine-phase one is discussed. Experimental results showing the effects of faults in multiphase drive on torque and current waveforms are presented, including their mitigation by the use of a post fault control method. This article also includes reliability calculations for the nine-phase motor drive in order to compare its lifetime with that of the three-phase conventional alternative.