Combination of Backstepping and Reduced Indirect FCS-MPC for Modular Multilevel Converters

In this paper, backstepping is applied as a first step of modulation control in the abc reference frame for modular multilevel converters (MMCs). In the second step, reduced indirect FCS-MPC is applied where the number of inserted modules are allowed to change by maximum one from the rounded result of the continuous outcome from backstepping. The backstepping method uses the ac-side current, differential current and summation of capacitor voltages in one arm as the state variables to form the Lyapunov functions. An established bilinear model of MMCs is used in the proposed design. The proposed approach offers similar dynamic performance as the full indirect FCS-MPC, at a much lower computational burden. The performance of the proposed method is validated by simulation.