Title:  Modeling and Control of Modular Multilevel Dc-DC Switched-capacitor Power Converter

Committee: 

Dr. Saeedifard, Advisor

Dr. Graber, Chair

Dr. Meliopoulos

Abstract:

The objective of the proposed research is to address the technical challenges associated with the design, operation and control of the Modular Multilevel Clamped Capacitor Converter (MMC3). The MMC3 is an attractive switched capacitor DC-DC converter topology for applications with high output/input voltage conversion ratio, featuring reduced voltage stress of power devices, high power density, bi-directional power flow capability and a modular structure. However, to fully exploit its advantages, an effective closed-loop control on its output voltage, the elimination or reduction of large-amplitude current spikes and a procedure to reliably bypass/insert its submodules during operation are desired. To this end, first of all, a detailed time-domain model along with a small-signal state-space model have been derived for the MMC3. A closed-loop voltage control strategy for the MMC3 has been proposed based on the developed models, which regulates its output voltage by utilizing the impact of the Pulse Dropping Technique. The developed models and proposed control strategy are validated by both simulation studies in MATLAB/Simulink environment with the PLECS toolbox and experimental studies on a compact 40-W MMC3 prototype designed and built with GaN FETs. Further improvement and optimization will be implemented in the future work.