Integrated control strategies of modular multilevel converters using arm current control in back-to-back systems

This paper presents two different capacitors´ voltage control schemes for modular multilevel converter (MMCs) with the application for back-to-back systems. Based on the derivation of the relationship between arm currents and active power of the MMCs in back-to-back system, the proposed scheme controls the currents of upper and lower arms independently in MMCs to achieve arm voltage balancing of capacitors of MMCs. As a result of directly controlling the arm currents, the proposed method can also naturally eliminate the inner circulating currents in the MMCs. The effectiveness of the proposed control schemes were experimentally verified using a 10 kVA three-phase MMC based back-to-back laboratory prototype.