Abstract: SCR-based current source converters are used in medium-voltage high-power (MV-HP) applications due to their ruggedness, reliability, low losses, and cost-effectiveness. However, they are not fully controlled devices and are typically used as line-commutated rectifiers or load-commutated inverters. They also produce quasi-square wave currents, which introduce significant lower-order harmonics. In CSI-fed drives, these harmonics result in low-frequency torque pulsations, particularly during startup and low-speed operation. On the grid side, SCR-based rectifiers draw distorted currents and operate with a lagging power factor, leading to higher total harmonic distortion (THD) and increased reactive power demand.

This work proposes a harmonic-minimization PWM technique for a 12-pulse CSI-fed multiphase induction machine drive to reduce lower-order harmonic torque ripples. The motor has an additional low-voltage winding connected to a small-power-rated voltage-source inverter (LV-VSI). This VSI assists in commutating the CSI-SCRs from the motor side, enabling PWM operation without requiring high-voltage, high-power external commutation circuitry. On the grid side, a three-phase four-winding transformer with a low-power, low-voltage VSI-assisted commutation scheme is used. Using a similar LV-VSI-assisted commutation, PWM operation of SCR-based current-source rectifiers is achieved, along with phase-advanced control of one rectifier. This allows one rectifier to operate at a leading power factor and the other at a lagging power factor, resulting in cancellation of fundamental reactive power, minimization of dominant harmonics, and a near-unity fundamental power factor at the grid.

Event Details
Title: Low Voltage Vsi-Assisted Commutation In Medium Voltage Scr-Based Current Source Converters For Drive And Grid Performance Improvement (PhD Viva Voce)
Date: July 09, 2026 at 10:00 AM
Venue: Google Meet (https://meet.google.com/xne-cncr-kib)
Speaker: Mr. Pratyush Pandey (EE20D027)
Guide: Dr. Kamalesh Hatua
Type: PHD seminar

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