EMC in power electronics - Sources of disturbance, couplings, SEM

The principle of electromagnetic compatibility (EMC) is to allow the correct and optimal operation of any electrical device in the presence of others, each in nominal operation. In other words, the right to "live" without "disturbing" one's neighbor. Three areas of interest flow from this definition: the study of disturbance sources, the study of coupling and, finally, the study of the impact of disturbances on a "victim", the field of electromagnetic susceptibility (EM). In this article, we apply this problem to the field of power electronics. The article will be devoted to reduction methods and simulation.

The operation of a static converter is intrinsically polluting, since electrical quantities are highly variable, over very short timescales (1 µs to 10 ns), with high amplitudes (of the order of kilovolt and kiloampere) and frequencies that can be high (100 Hz to 1 MHz). More than their amplitude, it is the derivatives of these quantities that are the source of electromagnetic disturbances. Indeed, all coupling phenomena operate in proportion to the derivative of an electrical quantity.

If we observe the electromagnetic disturbances emitted by a static converter on a frequency scale, as shown below, we see that they are spread over 7 decades. In fact, each converter stage contributes to disturbance over a frequency range depending on its switching frequency: the input rectifier up to a few 10 kHz, the HF switching stage up to a few megahertz, and phenomena linked to switching transitions (resonances, excitation of eigenmodes) up to a few tens of megahertz.

Moreover, the widespread use of static converters in consumer equipment is multiplying the sources of pollution. The problem of EMC in power electronics therefore consists in acting on the temporal characteristics of signals to limit their spectral range, or to try to confine all undesirable parasitic effects within the converter.

The work presented in this article reflects a twofold concern: to understand and analyze parasitic phenomena, in order to better control them and reduce their harmful effects, and also to find industrially applicable solutions and design rules, in view of the highly restrictive EMC standards to which all electrical equipment in the EEC (European Economic Community) has had to comply since 1 ^er January 1996.

The focus of this article is on static conversion, so efficiency criteria are obviously an inescapable imperative. However, we wanted...