A minimized AC circulating control strategy for a non-isolated modular multilevel DC/DC converter

Intermediate AC transformers are commonly used in high voltage high power DC transformers which are used for medium and high voltage DC conversion and interconnection of DC power grids. These bring greater loss and volume. In this paper, a non-isolated multilevel modular DC/DC converter is studied. The converter avoids the need for an AC transformer compared with the common dual active bridge DC/DC converter. This paper first analyzes the working principle of this converter and establishes an equivalent mathematical model. Because of the special imbalance of the sub-module capacitor voltage, the converter needs to introduce an AC circulating current. A minimized AC circulating control strategy is proposed, which ensures the power balance of the bridge arm, reduces the AC component of the bridge arm current and the loss of the converter. The performance of the converter and the effectiveness of the proposed control strategy are verified in a Matlab/Simulink simulation. Finally, an experimental platform is built to verify the effectiveness of the converter topology and the control strategy. © 2021 Power System Protection and Control Press.