Characteristic analysis of switching voltage power spectra under the mode of random carrier-frequency modulation

摘要

Purpose - The purpose of this paper is to provide a theoretical platform for studying therncharacteristic of random carrier frequency (RCF) modulation and analyze the related parameters inrnterms of electromagnetic interference (EMI) suppressing.rnDesign/methodology/approach - In this paper, the expression of the amplitude of switchingrnvoltage power spectra under the RCF mode is presented. According to the expression, the effectivenessrnof related parameters on EMI mitigation is discussed. Theoretical predictions are confirmed with arnclosed-loop boost converter which power is 7.5 W and nominal switching frequency is 200 KHz.rnFinally, special attention has been paid to output voltage ripple.rnFindings - Under RCF scheme, with increasing of random degree, the spectrum of switching voltagernis dispersed, so the power spectrum density amplitude of switching voltage falls, and then the level ofrnEMI is lowered. This theory shows that the voltage power spectrum density attains maximum whenrnd = 0.5, so in the spread spectrum modulation, the duty cycle of 0.5 should be avoided in terms ofrnconducted EMI mitigation.rnOriginality/value - The analytical expression of switching voltage power spectra under the RCFrnmode is presented, providing a theoretical platform for the related research. The selection of duty cyclernhas effect on EMI level is put forward for the first time. Voltage ripple is discussed in close-loop circuit.