Differential mode (DM) current ripple EMI noise analysis for three-phase Vienna type rectifiers

For a Vienna rectifier, the phase-leg's pulsating voltage is the source for the input current ripple and Electromagnetic Interference (EMI) noise. Double Fourier integral transform is commonly used to determine the harmonic spectrum of the phase-leg voltage so as to predict EMI noise. For three-phase, three-level rectifiers, like the Vienna rectifier, this process can be very cumbersome and can vary depending on the modulation scheme used. Moreover it doesn't give direct estimate of the current spectrum which is needed for filter design as the limits of noise current spectra are given in many EMI standards. Hence, for designing the filter for the DM noise, detailed analysis of the DM ripple current is very important. In this paper, the DM ripple current in Vienna type rectifiers using a dual stacked carrier based modulation scheme is investigated and the technique to predict the worst current ripple is developed. Based on this worst current ripple, the method of finding the attenuation requirements for EMI filter design is also described. Simulations were conducted to validate the worst current ripple predicted using the proposed technique.