Modular Multilevel DC Cascaded Converter with Battery Electrical Storage Integration

Abstract

Medium voltage dc microgrids seeks to compete with conventional ac systems by providing various benefits regarding electrical power availability and efficiency. One method of achieving this goal is to provide a more effective and reliable interface to renewable energy sources and es pecially electrical storage devices. This paper presents a multilevel, cascaded converter topology that allows for the integration of various low voltage power sources and storage units into a single string of series connected half-bridge submodules. The resulting topology allows the system to function as medium-voltage dc voltage source. By implementing an additional, nestled current loop, guided by passive tuned filters, the converter controls the power flow between the submodules and the system, thus achieving power balance in all operating modes. This paper presents the underlying converter control principle for configurations containing electrical battery interfacing devices. Simulation and experimental results from a scaled prototype demonstrate the converters capabilities for a wide range of output power delivery.