A Comparative Study of Carrier-Frequency Modulation Techniqu(9)

Abstract—A rigorous mathematical analysis and a comparative study of carrier-frequency modulation (CFM) techniques for the conducted electromagnetic interference (EMI) suppression in pulsewidth-modulated converters is presented. CFM techniques dither the

626IEEETRANSACTIONSONINDUSTRIALELECTRONICS,VOL.49,NO.3,JUNE

2002

(a)

(b)

Fig.12.

PowerspectraoftheinputcurrentwithRCFMandBW

=200Hz.(a):RCFM,<=0:5.(b):RCFM,<=0:2.(c):

RCFM,<=0:1.(d):PCFM.

theperformanceofthetwoschemesaredifferent.Thetheoret-icalspectraofthediodevoltagewiththetwoschemesareshowninFig.13.Basically,RCFMgiveshigherlow-frequencyhar-monicsthanthePCFM.Noharmonicswillbegeneratedbeyondthesidebandofthefirst-order-switchingharmonicinPCFM[Fig.13(d)].Fig.14showstheoutputvoltageoftheconverterunderthetwoschemes.ItcanbeobservedthattheRCFMintro-duceshigherlow-frequencyvariationthanthePCFM,thuscon-firmingthetheoreticalprediction.Althoughlow-frequencyhar-monicsintheRCFMcanbereducedwitha

smaller