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arXiv · 2507.10086

Fast-Response Variable-Frequency Series-Capacitor Buck VRM Through Integrated Control Approaches

Guanyu Qian·Haoxian Yan·Xiaofan Cui
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Abstract

Fast-response voltage regulation is essential for data-center Voltage Regulation Modules (VRMs) powering Artificial Intelligence (AI) workloads, which exhibit both small-amplitude fluctuations and abrupt full-load steps. This paper introduces a control scheme that integrates a linear controller and a nonlinear controller for variable-frequency Series-Capacitor Buck (SCB) converters. First, an accurate small-signal model is derived via a Switching-Synchronized Sampled State-Space (5S) framework, yielding discrete-time transfer functions and root-locus insights for direct digital design. A critical concern for SCB converters is series-capacitor oscillation during heavy load steps if the strict switching sequence is not maintained. To accelerate large-signal transients, a time-optimal control strategy based on Pontryagins Maximum Principle (PMP) relaxes the switching constraints to compute time-optimal switching sequences. A transition logic is then proposed to integrate the high-bandwidth small-signal controller and the large-signal controller. Simulations demonstrate a rapid output voltage recovery under a heavy load step-up, over ten times faster than a linear controller-only design. Preliminary hardware tests indicate a stable rejection to heavy load disturbances with zero steady-state error.

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Guanyu Qian, Haoxian Yan, Xiaofan Cui. 2025-07-14. Fast-Response Variable-Frequency Series-Capacitor Buck VRM Through Integrated Control Approaches. https://doi.org/10.1109/compel57166.2025.11121219

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