Abstract
Abstract In this paper conducted electromagnetic interference (EMI) of boost converter with switching frequency modulation (SFM) is theoretically analyzed in details. In the analysis line impedance stabilization network parameters, power inductor and input filtering capacitor parameters are taken into account. The analysis shows that the conducted EMI attenuation due to the use of SFM depends not only on modulation index as it is assumed in numerous research papers, but also on central switching frequency. Useful expressions to numerically calculate SFM boost converter conducted EMI spectrum and attenuation due to the use of triangular and sawtooth modulation waveforms are derived. Additionally experimental verification of the theoretical results is performed using a superheterodyne spectrum analyzer. Moreover a procedure for the choice of optimum SFM parameters (modulation waveform, frequency deviation and modulation frequency) to get maximum conducted EMI attenuation is proposed.
Highlights
Nowadays switch-mode power converters (SMPC) are often used in many electronic devices to convert electric power with high efficiency
To get the maximum electromagnetic interference (EMI) attenuation due to the use of Switching frequency modulation (SFM) for the given value of fsw, SFM parameters should be properly chosen. For this purpose a procedure for the choice of optimum SFM parameters to get maximum EMI attenuation is proposed as follows: step 1: choose fm slightly higher than resolution bandwidth (RBW); step 2: as m(t) choose sawtooth; step 3: calculate unmodulated VLISN spectrum using (1)-(5); step 4: calculate SFM VLISN spectrum using (1)–(4), (7), (10); step 4: calculate AEMI versus Δfsw using (13); step 5: find Δfswmax at which AEMI is at maximum; step 6: choose Δfsw= Δfswmax; step 7: end
The comprehensive theoretical analysis presented in this paper shows that the assumption that conducted EMI
Summary
Nowadays switch-mode power converters (SMPC) are often used in many electronic devices to convert electric power with high efficiency. Noticeable suppression of peak EMI levels can be obtained by the modulation of switching frequency fsw using simple periodic modulating waveforms (such as sine, triangle, sawtooth, etc) spreading the spectrum of SMPC voltages and currents [8],[9]. Numerous research papers [6,7,8,9,10,11] are devoted to SMPC conducted EMI reduction with periodic SFM, usually the analysis includes only the investigation of spectra of rectangular pulse trains (representing power component voltages) or power component currents (such as power inductor current). The analysis presented in the papers can omit several important details of the effect of SFM parameters on conducted EMI attenuation. In this paper a comprehensive theoretical analysis of conducted EMI of SFM SMPC is presented. Additional experimental verification is performed and a procedure for the choice of optimum SFM parameters to get maximum EMI attenuation is proposed
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