MODULAR MULTILEVEL CONVERTER-BASED TRANSFORMERLESS BATTERY ENERGY STORAGE TOPOLOGY

摘要

A modular multilevel converter (MMC)-based transformerless battery energy storage topology, each phase circuit thereof consisting of multiple subunits, connected in series, and composed of half-bridge power modules and battery power saving modules. The subunits connect to a power grid via a buffer inductor. Each phase is formed by an even number, n, of serially connected subunits that are divided into a top group and a bottom group, the number of subunits in each group being n/2. In the topology, the output phase voltage level ladder number is n/2+1, and the line voltage level is n+1. The output terminals in each phase are the midpoints of the two groups of units, and between the output ends and each unit are coupled or non-coupled inductance connections. The topology is connected in parallel on the power grid, and can thereby control power pollution from the grid, compensate for photovoltaic or wind power instability, and provide sine wave voltage that is uninterrupted, clean, stable, of high quality and a consistent frequency.