Optimal Cell Utilization for Improved Power Rating and Reliability in a Grid-Scale Three-Phase Battery Energy Storage System Using Hybrid Modular Multilevel Converter Topology Without Redundant Cells

Redundant cells within a battery energy storage system (BESS) are an important aspect to be considered in a BESS planning, design, and operation in order to achieve high reliability. The conventional topology does not have the ability to take advantage of its idle cells, at least one-third of its cells are constantly idling in a typical three-phase BESS. This article presents a new topology for a three-phase grid-scale BESS, where it offers three ways to deal with its idle cells. First, the idle cells were eliminated from the BESS plant while still achieving the desired output power with reduced cost. Second, the idle cells were utilized where no redundant cell is required. Finally, they were utilized to meet the output power required during peak demand. Consequently, the overall construction cost of BESS plant, losses, size, and control complexity are reduced while the reliability is improved. The simulation results indicate that at least 140 out of 333 modules (3996 cells) are in an idle state during the BESS operation, with the three-phase output voltage achieved in both topologies. Using 333 modules, the three-phase output power has increased by 58.8% in the proposed topology (306 kW) compared with the conventional topology (180 kW).