Analysis and Control of Improved MMC With Symmetrical Super Capacitor Energy Storage System in EER Application

Energy storage system becomes one of key components in the medium voltage grid with the ever-increasing development of renewable energy resources. This paper proposes an improved modular multilevel converter (IMMC) where symmetrical super capacitor energy storage banks are interfaced to the three-terminal power unit through a Buck/Boost converter. Six typical operation modes are taken into account and the control algorithms such as state of charge (SOC) equalization and sub-module capacitor balance based on carrier phase shift sine pulse width modulation (CPS-SPWM) are developed. Finally., the analysis and control strategies are verified through the MATLAB/Simulink simulation results and down-scaled prototype experimental results.