Digital Variable-Frequency Control Enabling Sensorless Flying-Capacitor Voltage Balancing in Multilevel Buck Converters

Abstract

Multi-level flying-capacitor (MLFC) buck converters offer significant advantages for low-to-high power applications, including reduced device voltage stress, potential for smaller magnetic components, and improved output power quality. However, ensuring stability and balance of flying capacitor (FC) voltages remains a major challenge, particularly under varying load conditions and system non-idealities. This work proposes a digital variable frequency (DVF) control for MLFC buck converters. This control enables fast output voltage regulation and sensorless FC voltage balancing across a wide range of load currents in point-of-load applications. The proposed approach effectively eliminates FC voltage imbalances arising from non-ideal system behavior, even under heavy-load operation. Extensive simulations and experimental validation demonstrate stable operation and fast dynamic response under no-phase-overlap operation.