Power Electronic Modeling for EMC

So-called "power electronics" include components and architectures that are familiar to specialists in this field, as well as to students of electronics who have had the opportunity to study some of these structures. In this context, designing an electronic system that best reconciles the efficiency and performance of components, mainly switching transistors, is a difficult exercise. However, even if it leads to an efficient functional design, the exercise does not necessarily meet the needs and requirements of electromagnetic compatibility (EMC).

The scope of EMC is much wider than just power electronics signals. In particular, it requires assessment of the noise generated on power electronics supply lines by their switching. While this noise can be classically calculated on the basis of the functional design within the electronics' bandwidth, its out-of-band estimation, i.e. at frequencies much higher than those of nominal operation, requires a modeling approach specific to EMC. This discrepancy is often misunderstood: the EMC profession is not satisfied with an exemplary cross-check between a measured signal and a calculated signal, nor, paradoxically, is it of any interest. The aim of the EMC engineer is to predict an envelope of emission maxima for the electronics, which will provide a framework for the measurements that can be carried out on these electronics under various operating conditions. He or she must also take into account the dispersions and uncertainties inherent in the components and the designed structure, for all frequencies between a few hertz and several gigahertz. Establishing these limiting amplitudes, and ensuring the compliance of the electronics with the requirements of the systems to which they will be fitted, calls for the use of models that are not functional models, but EMC models.

By using fast, robust models that deliver comprehensive results without being overly prescriptive, and by positioning the EMC performance of electronics within a reliability and dependability analysis, the EMC engineer contributes to the design of power electronics from an angle that is not that of the hardware designer.

With this article, we hope to provide the first building blocks for the EMC engineer to develop the model he will have to build for the electronics he is in charge of.