Description

Abstract: Energy storage has become more popular in the electric power system over the last few decades due the large penetration of energy from renewable energy sources. Ancillary services such as load leveling, peak shaving, and voltage support are achieved using energy storage on electric grid. Conventional battery energy storage systems (BESS) rely on large battery banks made with long battery strings where several of them are connected in parallel. A two level or three level converter is used to convert the DC voltage of the batteries to AC. This kind of converter configuration is quite poor in harmonic performance and require large filters. Modular Multilevel Converters (MMC) provide a better solution for the existing problems. The battery bank is split into small units and distributed among the sub-modules (SM). The high number of SMs generate an AC voltage with multiple levels, thus with low harmonic losses. Due to the high number of switches and components in the converter, electromagnetic transient (EMT) simulation of this converter is computationally intensive. This research proposes a detailed equivalent model which can be used to efficiently simulate an MMC with embedded storage. The accuracy of the model is validated against a detailed implementation of the MMC and a prototype experimental setup.