非隔离型模块化多电平DC/DC变换器的最小化桥臂环流控制

用于中高压直流电压转换和直流电网互联的高压大功率直流变压器一般采用中间交流变压器，存在损耗高和体积大等不足。对一种非隔离型的模块化多电平DC/DC变换器进行了研究，与普通双有源桥式DC/DC变换器相比，避免了交流变压器的存在。首先分析了此变换器的工作原理，建立了变换器的等效数学模型。考虑子模块电容电压存在特殊的不平衡，变换器需要引入交流循环电流，提出了一种保证桥臂功率均衡的最小化桥臂环流的控制策略，减小了桥臂电流的交流分量，降低了变换器的损耗。在Matlab/Simulink中仿真验证了变换器的性能和最小环流控制策略的有效性。最后搭建实验平台进行了实验验证。

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. This work is supported by the National Natural Science Foundation of China (No. 51777216), and the Natural Science Foundation of Shandong Province (No. ZR2018MEE040 and No. ZR2019MEE094).