An Enhanced Multi-frequency Small-Signal Model for a High-Bandwidth PCM Buck Converter

An enhanced multi-frequency small-signal model (E-MFSSM) is proposed to analyze the frequency domain characteristics of high-bandwidth peak current mode (PCM) buck converters. For such systems, the small-signal averaged model (SSAM) fails due to three major factors (i) the sampling-hold effect produced by the PCM control (ii) the considerable sideband components that exist in the pulse width modulation (PWM), and (iii) the large modulation waveform ripple due to the high bandwidth. Several modified small-signal models have been proposed by considering factor (i) or (ii). Compared with these models, our E-MFSSM incorporates all three factors to make further improvement in accuracy. In this study, factors (i) and (iii) are modeled by describing function. By considering the dominant sideband component, factor (ii) is added to obtain this extremely accurate model. Simulations and experiments are presented as verifications.