Comprehensive analysis of filter inductor asymmetry on conducted emissions in buck and boost converters

Abstract

Increased edge rates and switching frequencies have led to higher efficiency and increased power density for dc-dc converter topologies utilizing wide band-gap (WBP) devices. These improvements in intended behavior come with a cost in the form of elevated EMI profiles and higher magnitude CM currents, which cause challenges in fielded systems. Therefore, there is an increasing need to model the CM behavior for these systems and provide efficient EMI mitigation techniques. A method to decompose a system’s mixed-mode (MM) behavior into its differential-mode (DM) and common-mode (CM) behavior is utilized in this thesis. This thesis analyzes the role of filter inductor asymmetry in decreasing emissions in common dc-dc converters while preserving the intended behavior of these systems. The proposed decomposition method is applied to buck and boost converters. This method produces common-mode equivalent models (CEMs) that provide simplified expressions for the CM behavior of systems. CEMs are developed for both simplified and practical implementations of the considered topologies. Analysis of these CEMs reveals that both converters demonstrate similar CM behavior trends for the simplified models but exhibit different CM behavior trends for the practical models. Two prototype buck converters are then utilized to empirically validate the CEMs for this topology. A low-power prototype is utilized to validate the simplified model. This example demonstrates the necessity of considering high-frequency voltage ripple to accurately represent the CM behavior of this topology. A high-power prototype is utilized to validate the practical model. This example demonstrates the sensitivity of a fielded system to unintended couplings with the grounding network.