Power Density Optimization of EMI Filters for Power Electronic Converters

The switching power converters are used in a broad variety of applications, from the consumer electronics to the DC distribution systems, from the vehicle applications (road vehicles, marine vehicles, aircraft) to the industrial automation. In each of these application fields, the conversion systems which present more compact size and reduced weight, at the same power, are strongly required in relation to stringent design constraints. In this context, the optimization of the power density of the converter becomes an essential requirement. The increase of the switching frequency of the static devices allows an improvement of the power density, thanks to the possibility of reducing the sizes of the energy storage passive components (inductors and capacitors). On the other hand, the increase of the switching frequency determines, with high probability, the generation of more relevant conducted electromagnetic interferences (EMI) in the frequency range 150 kHz – 30 MHz. In particular, the high switching frequency is responsible for several serious problems affecting both the reliability and the electromagnetic compatibility of the systems of which the converter is part. For this reason, noise mitigationg is, more than ever, one of the major issues in power electronic system design, particularly when dealing with stringent standard regard the maximum emission limits, which however are mandatory for the marketing of these systems. EMI filters are the most efficient among the different possible solutions to mitigate the conducted electromagnetic interferences. On the other hand, EMI filters are part of the power electronic converters and they have significant impact on the overall converter volume and weight. In order to take on this issue, besides satisfying EMI limits, a further optimization in terms of filter size and weight during the design stage is advantageous to maximize the overall converter’s power density. The identification of the configuration leading to the best power density, in terms of minimum volume/weight, is a nontrivial task. The conventional design of EMI filters disregards the power density issue. The trial and error approach requires a significant effort in terms of time spent and it does not guarantee the optimal choice of filter configuration in order to obtain the maximum power density. For this reason, an automatic optimized design procedure of discrete EMI filters has been developed. Once the power electronic converter characteristics are known and based on databases, suitably set up, of commercially available devices for the realization of EMI filters, the optimized procedure enables EMI engineers or scientists to obtain the best EMI filter configuration in term of power density. On the basis of the developed automatic design procedure, an interactive software, ODEF (Optimized Design of EMI Filters), has been developed to make the new design procedure more accessible to EMI designer. Moreover, the developed application is provided of a graphical interface which allows to analyze and compare simultaneously different EMI filter designs. The optimization algorithm can be used as a EMI filter design tool but also as a tool for the analysis of the EMI filters performance.