Indirect Control of Capacitor Voltage Ripple and Circulating Current in a Modular Multilevel Converter

Model predictive control is a promising approach to control a multi-objective modular multilevel converter (MMC). In this approach, the control objectives of MMC are included in a single cost function and evaluated for all possible switching states by using weighting factors. The complexity of weighting factor selection process increases with the number of control objectives, and it affects the performance of MPC as well. To reduce the dependency on the weighting factors, a new model predictive control with zero-sequence voltage injection is proposed. With the proposed approach, some of the control objectives like reduction of submodule capacitor voltage ripple and circulating current can be achieved without using a cost function. The proposed approach also reduces the total harmonic distortion of the output voltage and current waveforms. The performance comparison of the proposed and existing MPC approach has been verified through MATLAB simulations on a three-level flying capacitor (3L-FC) based MMC system.