Active Current and Energy Control for the Quasi-Three-Level Operation Mode of an Extended Modular Multilevel Converter Topology

Recently, a Quasi-Three-Level Operation Mode for a new modular multilevel converter topology has been proposed. This paper presents a fundamental improvement of this operation mode which is achieved through a closed-loop branch current and energy control. The proposed approach uses the available degrees of freedom of the topology to actively balance the energies of the input capacitors and module capacitors. Moreover, the branch currents are controlled during both constant output voltage levels and transitions. In comparison to the operation mode from the literature, the proposed approach enables a stable operation with reduced input capacitances, module capacitances, peak branch currents, and converter losses. This is validated through simulations.