Audiosusceptibility Calculation in One-Cycle Controlled DC-DC Converters Based on the Describing Function

Audiosusceptibility of a buck converter employing on-cycle control is investigated using the describing function method. First, the one-cycle control principle is presented and then the describing function method is briefly discussed. The describing function method is applied to a one-cycle controlled buck converter in order to derive the audiosusceptibility transfer function. The procedure is implemented in Matlab and then the Caspoc simulations validated the correctness of the theoretical considerations. The results provided in Caspoc simulation, both for the magnitude and phase characteristics, overimposed with good accuracy on the Bode diagrams calculated in Matlab, and therefore an excellent match between the two diagrams is observed. The existence of a critical frequency where a perturbation in the input voltage is least attenuated is revealed and has to be considered in converter design.