Conducted electromagnetic emissions in unity power factor AC/DC converters: comparison between PWM and RPWM techniques

A PWM unity power factor AC/DC converter generates harmonics at switching frequency and its multiples in radio frequency (RF) range. This concentrated power spectrum may produce electromagnetic interference (EMI) problems. In this paper, the random pulse width modulated (RPWM) technique is used in order to distribute the noise spectrum over a wide range of the frequency domain. Thus, amplitudes of these harmonics decay and EMI problems are reduced. An AC/DC converter with sinusoidal input current and a line impedance stabilization network (LISN) are considered to study the RF noise emanating from the converter. A noise model to study the EMI problem is presented and used in this study. A unity power factor AC/DC converter with two different controls: PWM and RPWM, has been implemented. To carry out noise compliance measurements a simplified LISN has been used. Experimental results confirm the simulation results and show the effectiveness of applying the RPWM technique in reducing the RF noise level