An Induction Machine With Tapped Stator Windings for LCI-Fed Medium Voltage Drive Applications

Abstract

The search for thyristor-based load commutated inverter (LCI) fed induction motor drives for medium voltage (MV) applications has been ongoing since the past few decades, and several new topologies have been proposed. Low cost, better efficiency, and greater ruggedness are the definite advantages of these drives. Since leading power factor is an absolute necessity for load commutation, most of these drives supply additional auxiliary reactive power at the motor terminals. However, in MV applications, this would require the auxiliary source of reactive power (typically a capacitor bank or voltage source inverter (VSI)), also to be rated for MV. To overcome this issue, a new topology using a tapped stator winding induction machine is proposed in this article. Here, a low voltage tapping on the stator winding is used to connect a low voltage VSI which supplies reactive power to the machine. The LCI is used to provide all the active power required from the main stator terminals rated for the MV operation. This article describes the proposed machine and drive configuration and the vector control method for the LCI fed drive. Experimental verification is done using a 75-kW, 3.3-kV prototype machine with a 350 V tapping on the stator winding.