Capacitance Requirements in Three-Phase MMCs for LV Systems: Review of Different Minimization Approaches

This paper presents a review for different techniques of low frequency capacitor voltage ripple reduction for low voltage five-level Modular Multilevel Converters (MMCs). This study is performed on two MMC topologies: a conventional MMC topology, and a modified reduced capacitance MMC topology. Two possible control techniques have been discussed and compared with numeric simulation results in terms of capacitor voltage ripple, inductor peak current, switch peak and rms current. These control techniques are: circulating current injection and third harmonic voltage injection. This paper focuses mainly on the amount of capacitor voltage ripple reduction attained by each technique. Simulation results are obtained from 10-kW, 400V, 50 Hz three-phase five-level MMC.