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Digital average current (DAC) control of switching dc-dc converters with single-edge modulation (trailing-edge and leading-edge modulations) is studied in this paper. To calculate the average inductor current with minimum calculation time and appropriate precision, a new algorithm, called the four-point-mean (FPM) algorithm, is proposed. The DAC control laws with trailing-edge and leading-edge modulations are derived by using FPM algorithm, and their stabilities are studied. The subharmonic oscillation of DAC controlled switching dc-dc converters is investigated and analyzed. It is shown that both digital slope compensation and digital reposition compensation of the ac component of duty ratio for digitally controlled switching dc-dc converters cannot eliminate the subharmonic oscillation of DAC controlled switching dc-dc converters. Instead, a new method, called digital triangle compensation, for the elimination of the subharmonic oscillation of DAC controlled switching dc-dc converters is proposed and studied. Experimental results are given to verify the analysis results.
Date of Publication: March 2010