Typical impulses in power electronics and their EMI characteristics

Electromagnetic interference (EMI) characteristics are one of the most important aspects of a power converter. For purpose of topology evaluation and EMI filter design, the spectrum of the current and voltage impulses, which are sources of the conduction EMI, should be analysed. To calculate the spectrum of an impulse signal, Fourier analysis is commonly used. But with this method it is not easy to obtain simple and clear symbolic results for the syntheses of EMI filters. Using a graphical method, simple and clear results can be obtained which describe the upper limit of the spectrum envelope. Therefore, the typical current and voltage impulses in power electronics are analysed by using this graphic approach. Equations, which describe their spectrum envelope upper limit, are derived. Using these results, the EMI characteristics of the common topologies can be compared easily. Furthermore, the method enables an efficient EMI filter design.