Capacitor voltage ripple control based on decoupled power analysis in MMC

Modular multilevel converters generate high voltage ripple in the floating capacitors which increases the harmonic content of arm voltages and currents and consequently the losses and can degrade the control performance. In order to reduce this voltage ripple, a large capacitance is usually employed, but the size and cost of the submodules and the whole converter are increased. In this paper the voltage ripple is analyzed using a decoupled power approach and the circulating current and common-mode voltage required to minimize specific harmonic components of this voltage are obtained. A control design based on the capacitor ripple analysis is proposed and simulation results which validates the analysis and the controller design are shown.