| MS Seminar

Name of the Speaker: Mr. Tanmoy Dey (EE22S052)
Guide: Dr. Kamalesh Hatua
Online meeting link: https://meet.google.com/mcv-ugjx-ivw
Date/Time: 19th June 2025 (Thursday), 2 PM
Title: A Variable Switching Frequency PWM Technique to Reduce Conducted Emissions of SiC MOSFET Based Active Front End Converter

Abstract :

Wide-bandgap (WBG) device-based power electronic converters are evolving nowadays due to their high switching frequency and high power density. The conducted emission noise resulting from the switching frequency of the converter violates electromagnetic interference (EMI) standards. Large passive EMI filters are typically used to comply with the standards. The present work proposes a variable switching frequency-based modulation technique to attenuate the low-frequency conducted emission of the three-phase active front end (AFE) converter. The majority of frequency dithering methods ignore the issues related to the resolution bandwidth (RBW) of the spectrum analyzer. RBW refers to the bandwidth of the band-pass filter of the spectrum analyzer, which accumulates the energies of all frequency components falling within this band and displays a single frequency spectrum. While measuring the noise, it must be fixed at 9 kHz as specified by international regulations. This article addresses the impact of RBW on noise measurement, and a modification in the existing technique is also presented such that the noise spectrum of different frequencies does not overlap within a 9 kHz bandwidth to obtain maximum noise reduction. The proposed method has been implemented on a hardware prototype of 1.6 kW, 400 V, three-phase AFE converter operating with closed-loop vector control. A reduction of 16 dBµV and 7 dBµV is observed in the conducted emission noise for 400 Hz and 9 kHz RBW, respectively, and the results are compared with those of constant switching frequency operation. However, improper execution of the starting phase of the AFE converter can result in high inrush current spikes, potentially damaging semiconductor devices. Therefore, it is crucial to carefully manage the start-up process of the converter with precision. To address this, a simple and effective soft start-up method for the AFE converter has been developed in this work. This approach gradually ramps up the DC link voltage by increasing the duty cycle of the top switches, while keeping the bottom switches off. The proposed ramp-controlled start-up technique has been experimentally validated on the same AFE hardware prototype.