Model analysis, simplified control and sensitivity verification of modular multilevel DC–DC converter with parallel branches

In view of the modular multilevel topology with its uses in medium-voltage DC vessel integrated power systems, this paper deals with typical modular multilevel DC–DC converter (MMDC) topologies and AC control methods. In terms of DC control, a brief introduction is first made about a MMDC topology with parallel branches and its static characteristics. Then, an analysis is focused on the modeling of the MMDC and its model simplification. An optimal control strategy is proposed for the simplified model. Finally, the sensitivity of this system to model and parameter uncertainties is verified both theoretically and experimentally. The obtained results show that the proposed MMDC consisting of a heterogeneous full-bridge submodule and a parallel-branch structure can make the submodule voltage self-balancing and the range of output voltage wide. The use of an optimal control strategy based on a simplified model can lead the system to achieve good static and dynamic performance and robustness.