Modular Multilevel Converters with Module-Level Energy Storage for Medium Voltage Applications

Abstract

This dissertation is on Modular Multilevel Converter (MMC) converter design and analysis and its integration with energy storage at the low voltage module-level. The developed converter concept and topology can be used in various applications especially for the support of intermittent renewable energy resources. The general converter structure is analyzed and extended to include integrated energy storage suitable but not limited to medium voltage applications. The behavior of the idealized structure is analyzed to obtain equations that govern general converter behavior and identify possible control loops. Detail mathematical switching model is developed for the MMC converter with generalized module structure. The switching model is averaged to obtain a large signal model and then reduced to obtain lower order models suitable for sizing and optimization. Open and compensated closed loop current control is proposed and extended to include feedback loops needed for full control of integrated energy storage. General sizing procedure with the optimization aspects is then proposed and used on the example system to obtain the converter structure parameters. The example system models are then used to fine tune the control and structure parameters and investigate the converter behavior.