Reducing Conducted Emissions at the Output of Full-Bridge DCDC Converters with High Voltage Steps

Pablo González-Vizuete,María A Martín-Prats,Joaquín Bernal-Méndez

doi:10.3390/electronics10121373

Abstract

In this work, we analyze the impact of output filter design techniques aimed to reduce conducted emissions at the output of a DCDC power converter. A thorough analysis, based on high-frequency circuit models of the converter, is performed to assess expected improvements offered by different design strategies. This analysis is then confronted with measurements of conducted emissions at the output of a 300 W 48 V to 12 V Phase Shift Full Bridge (PSFB) prototype. Those experimental results demonstrate that a symmetric arrangement of the output LC filter and a direct bonding of the return output terminal of the converter to chassis are effective to reduce common mode conducted emissions at the output. Those results also demonstrate that the symmetry of the output LC filter can reduce conducted emissions in differential mode at high frequencies, where common mode to differential mode conversion is the predominant contribution to differential mode noise. However, direct bonding to chassis of the return output terminal may be ineffective at high frequencies due to the parasitic inductance associated with this connection. Main conclusions drawn for this analysis are applicable in general for isolated converters with a high voltage step between high and low voltage sides. Since the techniques of reduction of conducted emissions studied here do not increase the number of filter components, they are especially suitable for applications where high power density is an important requirement, e.g., aerospace or automotive applications.

Highlights

High efficiency and high power density are key requirements in power converters in several fields, such as automotive [1], aeronautics [2,3] and telecommunications [4]
This work analyzes and quantifies reduction on conducted common mode (CM) and differential mode (DM) emissions at the output power leads of a power converter achieved by design techniques based upon symmetric/asymmetric placement of components of the output filter of the converter
These design techniques have been applied to an isolated Phase Shift Full Bridge (PSFB) 300 W DCDC power converter with a high voltage step between the HV side and the low voltage (LV) side, for which highfrequency circuit models has been proposed to analyze key factors affecting CM and DM conducted emissions

Summary

Introduction

High efficiency and high power density are key requirements in power converters in several fields, such as automotive [1], aeronautics [2,3] and telecommunications [4] In this context, current trends are aimed towards the use of higher switching frequencies and fast switches (e.g., wide bandgap semiconductor switches) to reduce volume and weight of passives without increasing converter switching losses [5]. Rapid voltage and current changes associated with high switching frequencies increase electromagnetic compatibility (EMC) issues such as conducted and radiated emissions [6] This makes it necessary to optimize the design of the converters to ensure compliance with mandatory EMC regulations while avoiding weight penalties associated with filtering requirements. Effects of reduction of the equivalent noise sources at the input power leads of converters have been achieved by using current balancing techniques [11,13,14,15]

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Conclusion