This paper presents a multilevel, cascaded converter topology that allows for integrations of combined photovoltaic and battery storage units. The modular features of the system enable the series connection of PV panels that, in turn, have a parallel connection to a specified voltage level. These voltage levels stem from a series string of power electronic submodules. Likewise, low voltage energy storage units are interfaced to the upper arm of the system via identical converter modules and provide various directions of dc and ac active power flow, depending on the mode of operation. By implementing additional, nestled current loops, guided by passive filters, the system controls the power flow between the photo-voltaic string, batteries and the low voltage dc terminal. The enhanced level of power flow allows the converter to achieve both a controlled energy exchange as well as various auxiliary services in the DC system. This paper demonstrates three distinct types of power flow that are achievable with by combining the multilevel topology along with multifrequency operations. Simulation results from a representative system model are utilised to demonstrate the three possible modes of operation.

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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.

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In an input-series and output-parallel (ISOP) connected modular DC-DC converter, module shutdown and reactivation are required to increase system efficiency, input voltage range and reliability. Methods are introduced to implement these capabilities in the ISOP DC-DC converter system using additional external IGBTs and existing internal IGBTs. Comparisons of the shutdown speeds and thermal stresses are made for these methods over a range of input capacitance and experimental results are obtained to verify these predicted results. Finally, conclusions are drawn on the advantages and disadvantages of each method.@en