Delay effects in averaged modeling of PWM converters

Abstract

This paper describes improved averaged models for PWM converters operating either in the discontinuous conduction mode (DCM) or with constant on- or off-time control. For DCM operation, an intrinsic delay is identified to exist between a perturbation in the on-time of the switch and the resulting perturbation in the off-time. For constant on- or off-time control, an analytical model is derived for the modulator that shows interesting phase lead and nonlinear, frequency dependent characteristics. Inclusion of these effects results in new averaged models, which are accurate up to one-third of the switching frequency, and corrects for the large discrepancy exhibited by previous models.