High Step-Up/Down Ratio Isolated Modular Multilevel DC-DC Converter for Battery Energy Storage Systems on Microgrids

This paper presents the analysis and design ofa line interactive uninterruptible power supply (UPS) connected to a microgrid through a high step-up/down(bidirectional) dc-dc isolated modular multilevelconverter with a high input to output voltage ratio.Resonant switching is used on the MMC to improveoverall efficiency of the converter. The input source forthis converter is a set of series and parallel batteriesand the output of the converter is connected to amicrogrid. The proposed converter steps up the inputvoltage with a 1:15 conversion ratio, and steps down theinput voltage with a 15:1 conversion ratio. Atransformer is used to both isolate the converter and tofurther increase the step-up/down ratio.