Dynamical Characterization of Voltage-Mode Controlled Buck Converter Operating in CCM and DCM

The paper investigates the dynamical differences imposed by the continuous and discontinuous operation modes under direct-duty-ratio or voltage-mode control. The safe load and source profiles for CCM and DCM converters are derived. It is shown e.g. that the DCM converter is more prone to instability caused by the load, while the CCM converter is sensitive to capacitive loads. The safe source profiles are shown to be almost the same for both converters but the source interactions caused e.g. by EMI-filter are shown to be smaller in the DCM converter at the vicinity of the converter output filter resonant frequency. Even if a larger magnitude variation as function of input voltage is observed in the control-to-output transfer function in DCM, the variation of magnitude in the loop gain can be made equal for both conduction modes by a proper controller design.