Two control strategies of modular multilevel converter in rectifier side based on arm current under unbalanced voltage condition

摘要

Two control strategies for MMC in rectifier side based on arm current control are proposed in this paper. The strategies work well both under balanced and unbalanced voltage conditions. The proposed strategies have the following advantages: firstly, ac side current is well balanced under unbalanced condition by adjusting the active power flowing from arms to dc bus; secondly, arm current reference is obtained by using multi-hierarchy control method, which keeps voltage balance of SM capacitors better than that with the nearest level control; thirdly, circulating current is suppressed inherently, removing the need of the standalone circulating current suppressing controller. Simulation results based on PSCAD/EMTDC prove the effectiveness of proposed strategies.