Control and sizing of modular multilevel converter-based STATCOM with hybrid energy storage system for large-scale integration of wind farms with the grid

A configuration of energy storage system with STATCOM features (E-STATCOM) using modular multilevel converter (MMC) is presented in this paper. It helps to integrate large wind farms into the grid complying grid codes. The E-STATCOM has the capability to provide active and reactive power supports according to the requirements. The proposed topology can handle higher power at improved efficiency compared to the conventional converter-based configurations. The energy storage system (ESS) of E-STATCOM is formed with battery and ultracapacitor to meet the demand of both high-power-density and high-energy-density loads. Also, the combination can improve the transient performance and lifespan of the battery. In this paper, the integration of hybrid energy storage system (H-ESS) with the MMC to form an E-STATCOM and associated control-related issues are discussed. An algorithm to balance the state of charge among the distributed ESS is proposed. A procedure to determine size of the H-ESS is also discussed. The complete system is simulated in PSCAD, and the effectiveness of E-STATCOM is checked for the integration of a large wind farm with the grid.