With the attractive features of modularity

low harmonic and redundancy control

modular multilevel converters(MMC)have received much attention and research in the field of middle and high voltage. To begin with

the discrete state equation is derived for MMC. A new control strategy based on multistep model predictive control is proposed for circulating current suppression existing in MMC. It can realize multistep optimal control for circulation and reduce prediction computation effectively. Firstly

single step prediction can be performed using the circulation discrete state equation

and the number of inserted submodules(SM)is then determined that meets the requirement to make multistep circulating prediction. The final optimal inserted SM number is chosen to act on the converter for circulating reduction. The proposed multistep model predictive control uses a finite control set(FCS)generated from single step prediction optimal solution

which greatly improves the efficiency by reducing the computational times of multistep prediction. Finally

the performance of the proposed control strategy is evaluated based on the 201-level MMC time-domain simulation system in PSCAD/EMTDC. The simulation results verify the correctness and validity of the proposed control strategy.