Design Challenges of a ±50 kV Battery Energy Storage System (BESS) for MVDC Grids

Grid-connected Battery Energy Storage Systems (BESS) with voltage levels up to 600 V are well known from the application at AC grids and maritime shipping technology. A future tendency in the DC grid structure integrates Low-Voltage to High-Voltage. Medium-Voltage DC grids with voltage levels between ±10 to ±50 kV are a promising alternative to traditional MVAC grids, due to the higher power transport capability compared to AC. Also, there is no skin effect and capacitive current in DC approaches. BESS has gained increasing acceptance in microgrids, as they can effectively compensate for the temporary mismatch of energy demand and fluctuations of the production of large-scale renewable energy sources. However, it is noteworthy that up today, an MV grid-size BESS is not available in the market and there is a need for such battery (e.g., ±50 kV, with large bottleneck power from 100 kW and stored energy capability of 100 kWh) in order to increase the operational efficiency of the DC network. This paper presents the challenges of pioneering a ±50 kV battery. Discussion of the initial tests i.e., electrical, mechanical and safety design aspects, has been made. A direct connection to the DC-bus using a buck/boost DC/DC converter can be established because of the battery's design.