A Unified Frequency-Domain Model of Analog and Digital PWM DC–DC Converter Considering PWM Delay

In this article, the effect of the pulsewidth-modulation (PWM) delay on the stability of PWM dc–dc converters is analyzed. First, a unified frequency-domain model considering the PWM delay is proposed. Based on the proposed model, the physical mechanism of the PWM delay is the sampling characteristic of the modulation process rather than the digital controller. As the analog PWM (APWM) and digital PWM (DPWM) converters both have the modulation process, they both have the PWM delay. Then, the different stabilities of APWM and DPWM converters are compared, which are caused by the state feedback introduced by the output ripple in the APWM converter. As these differences are not caused by the additional time delay in the DPWM converter, when other parameters are the same, the DPWM converter is not always more unstable than the APWM converter. These influences are rarely reported in existing analyses of the modulation and can only be reflected by the proposed model. Finally, the stability of basic converters is analyzed by the proposed model. Compared with existing models, only the proposed model can reflect the different stabilities between the APWM and DPWM converters accurately, which is ensured by experiment results.