TITLE:
Improved Ladder Wave Modulation of Circulating Current Suppressing Control Strategy of MMC
AUTHORS:
Pinggang Song, Yunfeng Li, Lina Wang
KEYWORDS:
Modular Multilevel Converter; High Voltage Direct Current Transmission; Circulating Current; Module Changing Selection Algorithm; Double Frequency Negative Component
JOURNAL NAME:
Energy and Power Engineering,
Vol.5 No.4B,
November
15,
2013
ABSTRACT: This paper partitions the arm current of MMC into uncontrollable current and controllable current. The former is determined by the load that can’t be controlled by taking any control strategy. The later caused by the unbalanced total inserted voltage of three arms can be controlled by some improved algorithms. The conclusion based on the researching the essence of circulating current is reached that change the number of the inserted sub-modules in each phase can suppress the circulating current. Combined with the improved ladder wave modulation, a novel circulating current suppression strategy particularly for the inverter station is developed. The improved strategy can adapt to load changes and reduce the circulating current and output voltage THD of MMC ac terminals greatly without increasing any peripheral circuits. Finally, the simulation model of 100 submodules in each phase is constructed in MATLAB and the simulation results verify the correctness and effectiveness of the modified control algorithm.