An optimized high-frequency EMI filter design for an automotive DC/DC-converter

As a consequence of the limited space in automotive vehicles and the focus on effective and cost-efficient power electronics, the interest in fast-switching switched-mode power supplies is increasing. Such fast-switching devices generate high EMI emissions that must be attenuated to meet given EMC requirements. Typically, passive EMI filters are used to reduce the generated emissions of switched-mode power supplies. With the knowledge of the generated EMI emissions and the noise source impedance of the switched-mode power supply used a passive EMI filter can be calculated. This paper presents a design procedure for determining the required filter components to comply with given EMC requirements. However, the high-frequency behavior of the real system usually deviates strongly from the ideally calculated filter. This is a consequence of parasitics of the components used as well as couplings between the components. The effects of the parasitics of the EMI filter components and their influence on the attenuation of the filter are analyzed in this paper. As a solution it is shown how the filter performance can be optimized by changing the components and adding additional components with little parasitics to the basic EMI filter. In this paper, the developed EMI filter design with its high-frequency improvements is applied to a phase-shifted full-bridge DC/DC-converter.

I. Introduction

More and more electronic components are being used in au-tomotive vehicles. As a result of the limited installation space and the aim of reducing vehicle weight, the size and weight of such electronic components are playing an increasingly important role. The conversion of electrical energy in power electronic devices takes place through switching operations. In order to minimize the size and weight of efficient switched-mode power supplies (SMPSs), increasing switching frequen-cies with rapid transients are applied. However, this advantage of higher switching frequencies and transients is countered by higher electromagnetic interference (EMI) emissions in the high-frequency (HF) range. To ensure that each component within a vehicle can perform the desired function and is not disturbed by external sources of interference, emission limits are prescribed for each component. To meet the specified electromagnetic compatibility (EMC) standards, EMI filters consisting of inductors and capacitors are usually added to the SMPSs to reduce emissions. These passive filters are usually oversized. In order to get a well fitting EMI filter for a given SMPS a design procedure is derived in this paper, which is an extension of the literatures [1] and [2].