The Effect of Carrier Frequency Modulation of PWM Waveforms on Conducted EMC Problems in Switched Mode Power Supplies

Summary

Electromagnetic compatibility (EMC) remains an issue which can present many problems to designers of high frequency power converter circuits. Usual techniques for alleviating the problems of interference generation by power converters involve the use of screening materials and filters, however, the effectiveness of such measures depends on the frequency the interference and the power density at each frequency of interest. As pulse width modulation (PWM) generates high frequency harmonics at multiples of the switching frequency, modulation of the switching frequency may be used to spread the spectral power density present at these harmonic frequencies. This paper presents a technique of frequency-hopping spread-spectrum modulation which may be applied to switched-mode power converters (SMPC’s) to reduce the spectral power density at harmonics of the switching frequency. The influence of the peak frequency deviation, the modulation sequence length and the type of modulating sequence on the resultant spectrum are discussed. These prediction have been broadly confirmed in practice, with measurements carried our with an EMC pre-compliance test system.

Additional information

Notes on contributors

David Stone

David Stone

BEng Degree from the University of Sheffield and PhD from the University of Liverpool in 1985 and 1989 respectively. Presently works at the University of Sheffield as a lecturer in Power electronics and Motion control systems, where his current research interests include switched mode power supplies, EMC and DSP control of brushless motors. Dr Stone is amember of the IEEE and serves on the IEEE UKRI PEL’s committee. (Department of Electronic and Electrical Engineering., Mappin Street, Sheffield S1 3JD UK.)

Barry Chambers

Barry Chambers

B. Eng. and Ph.D. degrees in Electronic Engineering from the University of Sheffield in 1964 and 1968 respectively. Following a peroid at the University of British Columbia, Canada, he is currently a Senior Lecture in Communications Engineering at the University of Sheffield. His reserch interests include EMC studies, conducting polymers and other novel materials, electromagnectic modeling and computer-aided electromagnetic mesurement technique and he is the author of over 80 paper in these areas. He is a Fellow of the IEE and a Chartered Engineer.