An Asymmetric Nine-Phase Induction Motor for LCI-Fed Medium Voltage Drive Applications

This article presents a new asymmetric nine-phase induction motor-based load commutated inverter (LCI)-fed drive configuration as an alternative to the popular LCI-based synchronous motor drive topology in medium voltage (MV), high power applications. The proposed machine has three sets of three phase windings, two of which are designed to carry the rated active power from the LCI at MV levels. The other three phase winding is designed to handle all the reactive power requirement of the machine at a standard low voltage level from an insulated gate bipolar transistor (IGBT)-based voltage source inverter (VSI). The VSI also assists the LCI operation by supplying some additional reactive power required for safe commutation of the thyristors of the LCI. A smooth torque profile is also ensured by using the VSI to cancel out the low frequency harmonics in the quasi-square-shaped LCI currents. A laboratory prototype of the machine rated 75 kW, 1650/1650/400 V is designed and built to verify the proposed drive and the experimental results obtained are presented in this article.