Load and supply interactions in VMC-buck converter operating in CCM and DCM

The paper investigates the dynamical differences of load and supply interactions in direct-duty-ratio or voltage-mode-controlled buck converters in continuous and discontinuous conduction modes. The origin of the interactions is the system impedances such as EMI-filters, cabling inductances, additional capacitors and input and output impedances of regulated converters. The dynamical parameters i.e. phase margin and control bandwidth of the CCM and DCM converters are designed to be the same. It is shown that the sensitivity for interactions can be concluded from the measured frequency responses. The investigations show that a converter operating in CCM is more sensitive to capacitive loads than a converter in DCM, while the DCM converter is more prone to instability caused by the load. The supply interactions caused e.g. by an EMI filter are shown to be smaller in CCM converter except near the converter output filter resonant frequency, where the forward-voltage transfer function has an amplifying effect to supply interactions.