Pulse Train Control Strategy for a Series Capacitor Buck Converter in Discontinuous Conduction Mode

This paper proposes a Pulse Train Control (PTC) strategy for the Series Capacitor Buck (SCB) converter operating in Discontinuous Conduction Mode (DCM). Instead of synthesizing a continuous duty ratio, the controller selects between two preset duty ratios in each switching period, and the same binary decision is applied to the two interleaved phases with a 180∘ phase shift. A reduced one-dimensional control-oriented discrete-time map is derived from output charge balance to describe the control cycle-scale regulation dynamics. Based on this map, the bounded-regulation condition is established and the design roles of the pulse pair (DH,DL) are clarified. The regulated steady state is shown to be a bounded threshold-crossing periodic motion rather than a static equilibrium, and the evolution of pulse patterns with operating condition is interpreted through border collision transitions. Full switching model and experimental results from a 12-V-to-1-V prototype support the predicted high-pulse fraction trend, the multiplier-based local attraction assessment of annotated periodic pulse patterns, the input voltage-dependent ripple estimate, and the fast large-signal response under representative load step conditions.