Interphase $LC$ Resonance and Stability Analysis of Series-Capacitor Buck Converters

Hybrid switched capacitor power converters, such as the series-capacitor buck (SCB) converter, have intrinsic $LC$ resonant dynamics that might influence its control stability and transient response. This letter presents a systematic approach to analyzing this intrinsic resonant behavior, which can be classified into output $LC_{o}$ resonance and interphase $LC_{B}$ resonance based on common-mode and differential-mode decomposition. The impacts of coupled inductors on the resonant amplitude, frequency, and settling time during a step line transient are analyzed. The influence of intrinsic resonance on control stability is clarified, providing guidance for controller design. A two-phase SCB prototype was built and tested with discrete and coupled inductors under different operating conditions. All the analyses are verified by simulation or experimental results.