Modular Multilevel Converter based Hybrid Energy Storage System

A new configuration for integration of hybrid Energy Storage System (ESS) into a STATCOM is presented in this paper. The configuration offers STATCOM features and has ability to support active power at different time scale. The configuration can be called as E-STATCOM, where 'E' stands for Energy Storage. Here, the E-STATCOM is configured around a Modular Multilevel Converter (MMC). The battery is connected at the DC link of MMC through series connected DC DC converters. On the other hand, supercapacitors are connected in each submodule of MMC. The combination of battery and supercapacitor yields better transient performance, improved battery life-span and compact sizing of ESS. In this work, E-STATCOM is used to address some issues related to grid integration of Wind Energy Generating System (WEGS). Under MPPT operation, the WEGS generates fluctuating power which may affect voltage and frequency stability of the grid. Here, the E-STATCOM absorbs the fluctuation and provides smooth power to the grid, which ensures voltage and frequency stability. The proposed configuration is suitable for high power level, as well as, high voltage level compared to conventional two-level converter based solution. The complete system along with control algorithms are simulated in PSCAD and the results are presented. The simulation results show the effectiveness of the proposed concept.