Modeling of topologies, modulation and control of stacked DC bus multilevel converters

Power electronic converters are very widespread in industrial energy conversion systems at low voltage (480V) levels. To increase the ratings of power electronic converters while retaining acceptable efficiencies, operation at medium voltage is desired. Multi level converters are increasingly utilized for medium voltage applications to perform the function of low distortion ac waveform synthesis from a dc power source while limiting switching device voltage stress. The objective of this work is to provide averaged switching function based models for design-oriented analysis of stacked bus multi level converters.; The systematic approach developed here for modeling of the averaged input-output behavior forms the basis for switching device and capacitor sizing, optimal modulator selection, dynamic analysis and small signal modeling of control loops and regulator design for multi level converter systems. Analysis of numeric and algebraic models of dc stack current injection characteristics leads to the development of alternate modulation strategies designed to control harmonic content and voltage balance which are presented herein. These algebraic models are used to synthesize linearized dynamic transfer properties of closed loop do stack voltage regulators. This work presents the development of numerical and algebraic models for five level converters as well as closed loop modeling, simulation and hardware verification for a three level inverter system in both rectifier and inverter modes. The systematic modeling methods developed here have advanced the understanding of device and dc stack current flow in stacked bus multi level converters. Furthermore, this generalized framework can be applied to other power electronic converters.