Characterizing the Dynamics of the Peak-Current-Mode-Controlled Buck-Power-Stage Converter in Photovoltaic Applications

It is well known that the application of peak-current-mode (PCM) control produces highly desirable properties in the conventional or voltage-fed converters but requires to compensate the inductor-current loop for extending the active duty ratio beyond 50%. This paper investigates the dynamical properties and operational constraints of a PCM-controlled buck-power-stage converter in the photovoltaic (PV) applications. It has been already earlier noticed that the application of PCM control can make the converter unstable in the PV applications. The investigations reveal that the inductor-current feedback forces the open-loop converter to adopt the dynamic properties of a voltage-fed converter, and consequently, the stable operation is limited to the constant-voltage region of the PV generator. The developed small-signal models reveal that a right-half-plane pole appears in the converter dynamics, when the operation point enters into the constant-current region leading to instability. The stability can be restored by heavily compensating the inductor-current loop, which seriously removes the desired properties materialized in the conventional buck converter. The provided experimental evidence fully supports the theoretical findings.