Caracterización a altas frecuencias de Chokes de modo común para filtros EMI en aplicaciones aeroespaciales

Laburpena

In modern power electronics systems, high switching frequencies are employed to increase power density. This trend leads to a worsening of the problems of electromagnetic interference (EMI), which makes it difficult to comply with the regulations that limit the electromagnetic emissions of these equipment. In this context, proper design and characterization of the EMI filter over a wide range of frequencies can greatly help to keep noise emissions under control while at the same time preventing designed over-specification. This is especially important in applications where strict requirements of size and weight are combined with stringent electromagnetic compatibility (EMC) regulations, as for example in aeronautical applications. The work presented in this Memory is focused on improving the characterization techniques of common mode chokes, which are key components of EMI filters. We propose a lumped circuit of the common mode choke where not only the low frequency components are included, but also the parasitics that alter the performance of these components at high frequencies. A modal analysis of the common mode choke is performed based upon the proposed circuit model. We obtain analytical expressions of the frequencies of resonance and the transmission coefficients for the different connection configurations, and a connection that allows to analyze simultaneously the response of the common mode choke to the common mode and differential mode currents is identified. We develop a technique, based on the use of advanced search algorithms, to find the parameters of the high-frequency circuit model of the common mode choke that fit best the actual performance in the different experimental setups. The key of the proposed method is the availability of the analytical expressions, which means a significant decrease of the computational cost associated with these search algorithms. Different commercial common mode chokes haven been measured and the response predicted by the high-frequency circuit model has been compared with the measured responses. The main advantage that this measurement technique offers compared to techniques previously proposed in the literature is that it allows the characterization of a common mode choke from a single measurement that also does not require auxiliary circuits (such as balunes). The analysis performed for the characterization of common mode chokes has also allowed us to design an alternative technique to measure the differential mode response provided by a common mode choke. This alternative configuration is simpler than the configuration that is typically used for this purpose. The sensitivity of this configuration is analyzed against electrical and magnetic couplings that tend to appear in practical cases. Finally, this work also presents a novel technique that mitigates the magnetic coupling problems that common mode chokes cause in compact filters. We analyze the effect of conductive bands placed near a common mode choke have on the common mode and differential mode attenuation provided by an EMI filter, where the common mode choke is mounted. We design a shield whose particular structure makes it possible to significantly reduce the electromagnetic couplings between the common mode choke and the nearby capacitors without impairing the common mode choke behavior in other frequency regions. The main features of this shielding technique are that can be used on-site, and do not increase the weight, volume or cost of the EMI filter.