A CM Filter Configuration for Grid-Tied Voltage Source Converters

Common mode (CM) filters play a crucial role in determining adherence to conducted emissions (CE) standards for grid-tied voltage source converters. Design and implementation of such filters can be challenging since they depend on several factors like identification of CM noise paths, fidelity of passive components and discerning the frequency and amplitude of CM noise sources. In this article, a CM filter has been proposed, which uses passive components along with the converter's heat sink as a circulating return path for the CM currents. Based on the presented CM circuit models with the proposed filter, a detailed design process has been delineated for selecting the passive components required to realize the CM filter. Additionally, the heat-sink potential has been shown to be touch safe during both ideal and nonideal grid conditions with the proposed CM filter. CE spectral results measured using a commercially procured line impedance stabilization network and captured time domain converter operational wave forms for a 2-level, 3 phi grid-tied voltage source converter validate the functionality and effectiveness of the presented design.