Modular Multilevel Converter With Partial Energy Storage System for Frequency Support

Frequency fluctuation becomes one of the urgent issues with the ever-increasing penetration of power electronics converters in the grid. This paper proposes a modular multilevel converter with partial energy storage system (MMC-PESS) where the arm is comprised of the normal submodule(NSM) and the energy submodule(ESM). Based on analysis of the relationship between the number proportion of ESMs and energy storage charging/discharging power, the control strategies including virtual synchronous machine (VSM) control, state of charge (SOC) equalization and the Buck/Boost control are developed for frequency support by applying the energy storage system. Finally, the theoretical analysis and frequency support performance are verified by the simulation results.