Analysis and control of modular multilevel converter-based E-STATCOM to integrate large wind farms with the grid

High-level penetration of wind energy generating system shows a negative impact on the performance of the existing grid due to injection of fluctuating power generated by the wind farms. This study presents a configuration of E-STATCOM which is formed by integrating hybrid energy storage system (HESS) into a modular multilevel converter. The E-STATCOM absorbs the fluctuations of wind power and injects constant power into the grid. It also provides necessary reactive power support to maintain the voltage at point of common coupling within the specified limit. The HESS is formed by combining battery and supercapacitor, which gives high energy density, as well as, high power density features. A control methodology with the dynamically varying limits has been proposed to operate the E-STATCOM as per the requirements. Apart from this, the effect of HESS on the circulating current is analysed and the corresponding control algorithms are developed. The complete system is simulated in PSCAD/EMTDC and the results show its effectiveness.