Modified sliding-mode observer of capacitor voltages in Modular Multilevel Converter

This paper proposes a modified sliding-mode observer of capacitor voltages in Modular Multilevel Converter (MMC), only using the measured arm currents. The proposed strategy enables to obtain the individual capacitor voltages without any voltage sensors, reducing the number of sensors in MMC and simplifying its communication system. A theoretical analysis is shown to demonstrate the basic concepts of the observer. Results are included to evaluate the proposed observer under distinct operating conditions, including external disturbances, parametric variations and unmodeled dynamics.