EMI reduction in randomized boost rectifier

Low frequency harmonics injection into AC power supply and small power factor are the main disadvantages of conventional rectifiers. By using the high power factor correction circuits (HPFCC) the input current has a sinusoidal form and is in phase with the power supply voltage. By solving the problem of power factor with high frequency switching current mode control, another problem arises-that of high frequency harmonics generated in radio-frequency (RF) range by the converter. Therefore the problem of electromagnetic interference (EMI) must be appropriately treated as well. This paper deals with randomized pulse width modulation (RPWM) strategy for the boost rectifier. The randomized modulation principle is introduced in an ordinary PWM control unit which is widely used in unity power factor correction circuits. Introduction of the RPWM results in smaller increases of the total harmonic distortion (THD) in the input current and consequently neglected decreasing of the power factor. On the other hand, this approach causes the high-order harmonics spectral components to be significantly reduced and dispersed around ordinary spectral lines, which means reduced conducted EMI as well.