Randomized carrier PWM with exponential frequency mapping

Abstract

Pulse Width Modulation (PWM) and Sigma Delta attainable with respect to regular PWM. A limited number of Modulation (SDM) have been used in several high linearity, publications show, mainly from an experimental point of high accuracy power delivery applications such as DC-DC view, the advantages of SDM over plain PWM to solve EMI, power converters, audio and RF power amplifiers as well as in power factor and acoustic tones [1,3,9]. data converters. In this paper we present a particular class of Carrier Frequency Modulated PWM (CFMPWM), which Since RPWM methods have been mainly developed for spreads the tonal content of regular PWM uniformly in Power Electronics applications, theoretical procedures to frequency and reduces the baseband noise with respect to SDM estimate the spectral properties of a given scheme are mostly by up to 15 dB. The new modulation scheme preserves at the based on the time Probability Density Function (PDF) of the same time the high efficiency properties of PWM. An parameter to be randomized (namely, period, width, duty approximate method to estimate the spectrum of CFMPWM cycle). This analysis is more straightforward for digital signals with both deterministic and random modulation is also microcontroller based implementations, where PWM signal presented. Simulation results and experimental data are icrated based However,atim e P WM s ignal reported to analyze the spectral spreading properties of the is generated digitally. However, time PDF based analysis proposed CFMPWM scheme. poses serious limitations for continuous-time highfrequency, fully integrated implementations where the I. INTRODUCTION randomization possibilities are less flexible. Although SDM Pulse Width Modulation (PWM) and Pulse Density and RPWM have been compared against plain PWM, Modulation (PDM) -in particular Sigma Delta Modulation spectral content of SDM with respect to RPWM have not(SDM)-have been used in several high linearity and high been analyzed. Also, the selection of a randomization accuracy switched-mode power delivery applications such as technique and its associated PDF to obtain a prescribed DC-DC power converters, audio and RF power amplifiers[1-spectral profile has not been addressed before. Although the 4]. In several applications where conducted and radiated problem is not solvable for a general PDF, a statistical electromagnetic interference (EMI) is a concern, wide-band approximation is critical for noise shaping applications. shaped noise content of SDM is preferred to inherently tonal This aper is organized as follows: in section II an content of PWM. SDM is also preferred in low frequency

Novel random pulse position modulation for three-phase four-leg inverters

“…An effective approach to attenuating the discrete components in the power spectrum is random pulse width modulation (RPWM), which adds random signals with a certain probability distribution into switching signals. In Liaw and Lin, 8 the authors classify the existing random PWM methods into three types: (1) random switching PWM, 9,10 (2) random carrier frequency modulation (RCFM), 11–13 and (3) random pulse position modulation (RPPM). 14–16 Random switching PWM was the first proposed random PWM.…”