An SCR-Based CSI-Fed Induction Motor Drive for High Power Medium Voltage Applications

A new topology of a silicon controlled rectifier (SCR) based current source inverter (CSI) fed induction motor drive suitable for medium voltage (MV) drive applications is presented in this article. The requirement of forced commutation circuitry has been the major disadvantage of an SCR-based CSI-fed induction motor drive. The proposed drive uses an induction motor provided with an auxiliary isolated low voltage winding on the stator. The SCR converter is connected to the main winding of the motor rated for MV levels. A voltage source inverter (VSI) of a small rating connected to the auxiliary winding injects a required voltage to ensure safe commutation of the SCR inverter. This enables the drive to operate over the entire speed range without requiring additional external commutation circuitry. The VSI also compensates the low frequency torque harmonics due to the quasi-square wave CSI currents thereby ensuring a low ripple torque profile. The proposed drive is experimentally verified using a 37.5 kW, 1.65 kV laboratory prototype with a 400 V auxiliary winding.