A 12-Pulse LCI- and VSI-fed Hybrid Medium-Voltage Drive for an Induction Motor With a Tapped Split-Phase Stator Winding

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. This article proposes a new topology of an LCI-fed induction motor drive, specifically suited for high-power medium-voltage applications. The proposed drive uses a medium-voltage 12-pulse LCI supplying an induction machine with a tapped split-phase stator winding configuration. A low-voltage tapping is provided on each phase winding of the machine. The leading power factor requirement is met by using two low-power low-voltage VSIs connected to the tap terminals and providing the reactive power required to slightly overexcite the machine. As a secondary function, the VSIs also help in canceling out some of the low-frequency air-gap magnetomotive force (MMF) harmonics by injecting compensating harmonic currents, thus resulting in a low torque ripple. The proposed drive is experimentally verified using a 75 kW, 1.65 kV prototype split-phase machine with 178 V taps on each winding.