The Load Commutated Inverter (LCI) fed drive is preferred over Voltage Source Inverter (VSI) based drives in many medium-voltage high-power applications, mainly due to its ruggedness and structural simplicity. Over-excited synchronous motors are conventionally used in LCI drives since a leading power factor is a mandatory requirement for LCI operation. The synchronous motor can be replaced by an induction motor to obtain several additional benefits, provided the leading power factor requirement is satisfied by some means.

The presentation discusses a new topology of an LCI and VSI fed multi-phase induction motor drive specifically suited for high-power medium-voltage applications. The proposed configuration has superior features like smooth generated torque, reduced machine size, reduced losses, and high system reliability which make the drive a fitting competent for medium voltage high power traction applications. The LCI and VSI fault tolerance algorithms are developed for the proposed drive configuration which highly enhances the system reliability and makes the drive suitable for critical traction applications. Further, a VSI-assisted PWM CSI technique is proposed which reduces the low-frequency torque oscillations in a 6-pulse LCI-fed drive and offers a smooth torque profile in the entire operating regions