High efficiency power converters for battery energy storage systems

Renewable energy sources such as wind-turbine and photovoltaic power generators may make the power grid unstable due to their output fluctuations. Battery energy storage systems (BESSs) are being considered as a countermeasure for this issue. “BESSs” require bidirectional ac-to-dc and dc-to-ac converters, so improvement of the converter efficiency is desired to improve the efficiency of BESSs. This paper presents the performance of 100-kVA and 500-kVA converters for BESSs in practical use, and introduces the development and the verification test results of a real-scale (500 kW) single-star bridge cell (SSBC) based modular multilevel cascade converter (MMCC) which is expected to be a new converter topology for BESSs.