Analysis and Performance Evaluation of Nonlinear Ramp Feedforward Compensation for PWM Buck or Buck-Derived Converters

The feedforward PWM with nonlinear ramp in a buck or buck-derived dc-to-dc converter is analyzed. It is noted that the conversion ratio M(D) in line-to-output transfer function(audiosusceptibility) becomes negative and the amplitude is decreasing as line increasing. Although the amplitude is significantly reduced with this scheme as compared to one without feedforward compensation, it is not to zero as in the case of an ideal feedforward PWM buck or buck derived dc-to-dc converter. The dc and small signal model is developed and the maximum output voltage variation range in open loop is predicted. Experimental data were collected to verify the analysis and evaluation.