Electromagnetic Interference in DC-DC converters

While achieving very high conversion efficiency and small size, the high switching frequency in modern power converters are also responsible for the majority of the electromagnetic noise generation and emission in electronic systems.

The filters required to attenuate this noise to comply with required emission standards can be both large and expensive.

We therefore conduct research into improving analysis and prediction of converter noise levels and to design optimum Electromagnetic Interference (EMI) filters. 

 

Conducted electromagnetic interference analysis and filter design for isolated DC-DC converters

By Ishtiyaq Ahmed Makda

DC-DC converters are widely used in automotive, industrial, and renewable energy applications; such as, electric vehicles, uninterruptable power supplies, and fuel-cell applications. High-efficiency, low cost, and high power-density are some of the important design parameters for any converter design; however, they also need to comply with the strengthened electromagnetic interference (EMI) requirements. Therefore, optimized EMI filters are important to produce a competitive product.


In this PhD project, two well-known converter topologies– the Isolated Full-bridge Boost and the Forward converter – for the modeling, analysis and design of EMI filter are considered. The main objective is to provide a fundamental understanding of the generation of differential mode (DM) and common mode (CM) noise voltage-sources and the corresponding noise paths. In particular, the CM noise, due to the parasitic transformer winding capacitance, is mainly considered in this work. The DM and CM noise models of the aforementioned converter topologies are proposed and analyzed to analytically determine the required filter attenuation. The feasibility of the noise models and their analysis are verified by means of several experimental results.


The major outcomes of present research are: The DM and CM noises can be accurately calculated in the low-frequency range of conducted-emission, thereby substantially reduces designer’s dependency on the finished converter prototype unit. The transformer inter-winding coupling capacitance, in a hard-switched full-bridge boost and forward converter, barely contributes to any CM noise current in the converter. However, the same parasitic capacitance has a severe impact in a phase-shifted forward converter and contributes to large CM noise current in the converter.