A Hybrid Design Framework for Fast Transient and Voltage Balancing in a Three-Level Flying Capacitor Boost Converter With Digital Current Mode Control

Multilevel flying capacitor boost (MLFCB) dc–dc converters offer high power density even at high voltage gain, in which digital control can achieve fast transient, and high efficiency. However, the challenges remain in identifying simple yet useful analysis and design techniques to ensure stability and flying capacitor (FC) voltage balance under uniform sampling. This article proposes a hybrid framework for stability analysis and controller design in an MLFCB converter under digital current mode control (DCMC). Continuous-time (CT) small-signal models (SSMs) of an MLFCB converter are derived, which seem to closely resemble the SSMs of a traditional boost converter. Thereafter, a novel DCMC architecture is proposed, consisting of a type-II (output voltage) digital controller and a proportional FC voltage controller. With a slower FC voltage loop, the type-II controller is designed using the CT SSM, which fails to predict fast-scale instability while aiming for a higher closed-loop bandwidth. After that, a discrete-time (DT) modeling framework is developed, and the model accuracy is verified using SIMPLIS switch simulation. Using DT SSMs, a closed-loop stability analysis is carried out, and the digital type-II controller gains are further tuned to achieve fast transient performance with stability. A 100 W, 12/48 V three-level flying capacitor boost (3LFCB) converter prototype is developed, and the proposed DCMC is implemented using an field programmable gate array (FPGA) device. Transient performance and stability are demonstrated using experimental results, which are found to be consistent with the analytical predictions.