| Summary: | This paper presents a method for evaluating grid-connected battery energy storage system (BESS) designs. The steady-state power losses of the grid interface converter, the battery pack, and the balancing circuit are calculated. The reliability of each complete system is calculated using a Markov-based modeling approach that takes into account the built-in redundancy of the system as well as performance degradation caused by faults. Finally, a simple economic analysis based on capital cost and efficiency is used to provide a basis for direct comparison between competing system designs. Three design options for a 1-MW 1-MWh BESS connected at 11 kV are compared: a conventional BESS using parallel low voltage power blocks, a BESS using a high-voltage intelligent battery pack, and a BESS using a cascaded H-bridge converter. The results of the analysis indicate that additional power electronics included in the battery pack as part of the intelligent battery pack and H-bridge designs can enhance the reliability of the BESS by an order of magnitude under typical conditions, without increasing the overall cost of the system.
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