Development of a 500-kW Modular Multilevel Cascade Convertor for battery energy storage systems

Natural energy sources such as wind turbines and photovoltaic power generators cause instability of the power grid due to their output fluctuations. Battery energy storage systems (BESSs) are being considered as a countermeasure for this issue. A Modular Multilevel Cascade Convertor (MMCC) is one suitable circuit topology for BESSs, because each cell can control each battery's state-of-charge independently, and the level of generated harmonics is low enough to eliminate the AC filter normally installed in conventional two level converters. This paper describes the development of a real-scale (500 kW) H-bridge MMCC for BESSs and reports successful test results of the control functions with a scale down grid model and a 6.6-kV real-scale distribution line.