Augmented Design of DC/DC Modular Multilevel Converter Improving Efficiency and Reducing Number of SMs

This paper presents an augmented design method for the dc/dc modular multilevel converter considering the control (e.g., the phase difference between arms ac voltages) and hardware aspects (e.g., type and number of submodules (SMs)) of the converter simultaneously. The proposed augmented design determines the number of SMs and their types (e.g., half- or full-bridge) in each arm and phase difference between arms ac voltages that minimize the total converter losses. Computationally-efficient analytical and semi-analytical methods are proposed to estimate the conduction and switching losses. To verify the effectiveness of the proposed method, the losses obtained from the proposed analytical and semi-analytical methods are compared with the results of the detailed converter switching model implemented in the Simulink environment. The performance of the converter designed by the augmented approach is compared with the conventional topology in terms of total losses and the number of SMs. The comparative study showed that the proposed design method yields a converter with lower total losses and number of SMs. Moreover, the proposed design method extends the operation regime of the converter, especially when the dc links voltage levels are close; this extension is not possible in the conventional modular dc/dc converter.