A Capacitor Energy Fluctuation Suppressing Method for MMC-MTDC Systems with Droop Control

The dc-link voltage deviation in multi-terminal high voltage direct current (MTDC) systems caused by droop control under various transmission power significantly increases the fluctuation rang of capacitor voltages in modular multilevel converters (MMCs). The principles of floating capacitor energy fluctuation are analyzed in this paper and an improved control method, adaptively regulating inserted submodules to maintain the stability of the cascaded capacitor voltage, is presented. Simulation results verify the feasibility and effectiveness of the control strategy.

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