Impact of Periodic Switching Frequency Modulation control to reduce conducted EMI in Power Factor Converters

Spread spectrum clock generation techniques (SSCG) were originally developed to reduce EMI in communications and microprocessor systems working in the range of hundreds of MHz. Nowadays, the switching frequency of power converters has been increasing up to values that make feasible the application of such switching frequency modulation techniques to reduce EMI emissions in power converters. Although random modulations have been applied before to power converters, periodic patterns can provide some advantages. The principle of this methods is shown and confirmed with experimental results obtained from tests carried out on a power converter. It is a 600 W boost converter switching at 40 kHz. Attenuations obtained in conducted EMI are evaluated, even under discontinuous conduction mode. Finally, special attention has been paid to converter efficiency, input current distortion and output voltage distortion in order to evaluate possible unwanted side effects produced by this technique