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

TSEetal.:CARRIER-FREQUENCYMODULATIONTECHNIQUES

(a)

(b)

parisonofthepredictedpowerspectrawithBW

=12kHz.(a)f=1:5kHzand =8

.

Fig.10.ImplementationoftherampVCO.

Low-frequencynoisewillinherentlyintroduce

when

isbasedontheharmonicspreading

effectsandthelow-frequencynoiseinjection.

III.EXPERIMENTALVERIFICATIONSANDCOMPARISONSThesameconverter,astabulatedinTableII,isinvestigated.CFMisachievedbyusingtherampvoltage-controlledoscillator(VCO)showninFig.10.Byintegratingthesignalthatcombines

amodulating

signal

(whichiseitherperiodicorrandom)

and

625

(a)

(b)

Fig.11.MeasuredpowerspectrumoftheinputcurrentwithPCFM(10dB/div).(a)f=6kHz,and =2.(b)f

=24kHz,and =8.

areferencedc

voltage

,atriangularwaveformisgenerated.Thepeak

valueoftheoutputisdefined

as

(27)

where

equals.Thetheoretical

andmeasuredresultsareshowninFig.12.

ComparingFig.11withFig.12,bothPCFMandRCFMgivesimilarprofilesinthemeasuredspectra,especiallyinthehigh-frequencyrange.However,forthelow-frequencyharmonics,