Control Strategy for On-line Smooth Connection of Passive Modular Multilevel Converter Station via DC/DC Converter into DC Grid

doi:10.3969/j.issn.1000-7229.2018.05.004

Abstract

Abstract: ABSTRACT： The modular multilevel converter （MMC） based DC grid is becoming an important trend in the electrical power system. But there is no mature strategy on on-line smooth connection of passive MMC station via DC/DC converter into DC grid. If the unlock sequence or control strategy is not appropriate, there will be a higher inrush current and the original operation of the system will be affected. Firstly, the design method of active power reference value before and after the connection of DC/DC converter and passive MMC station is analyzed. Secondly, the equivalent circuit of DC/DC converter and passive MMC station is analyzed. The change of the capacitor voltage of the sub-module before and after de-locking is analyzed, and the DC voltage matching control strategy is put forward to decrease the inrush current at the de-locking moment. Finally, taking the smooth connection as target, the overall control strategy process is presented. A model of five-terminal symmetrical bipolar DC grid with DC/DC converter is built in PSCAD/EMTDC, and the simulation results validates the effectiveness of the proposed control strategy.

Key words: modular multilevel converter （MMC）, DC grid, smooth connection, DC/DC converter

CLC Number:

HAN Naizheng, JIA Xiufang, XU Jianzhong, ZHAO Chengyong . Control Strategy for On-line Smooth Connection of Passive Modular Multilevel Converter Station via DC/DC Converter into DC Grid [J]. Electric Power Construction, 2018, 39(5): 28-.

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