Indirect MPC method with improved output voltage and current waveforms for MMCs

Abstract

This paper focuses on a nonrequired weighting factor tuning task model predictive control (MPC) approach with improved steady-state performance, resulting in better harmonic distortion in output current and voltage for a single-phase modular multilevel converter (MMC) system. For the proposed indirect MPC technique, two independent control stages are designed to achieve various control objectives at once without the use of weighting factors. The first stage includes a single cost function, only related to the output current to generate a temporary quantity of inserted submodules (SMs). A circulating current regulation using predicted value is proposed to obtain the total quantity of inserted SMs regarding the circulating current suppression. The final quantity of inserted SMs is adjusted and generated from the temporary quantity to be used in a voltage sorting algorithm. Without the use of weighting factors, the control objectives in the MMC system can be achieved using the proposed indirect MPC. The output current and voltage have a considerable improvement over that of the conventional indirect MPC. The simulation and experimental outcomes validate that the proposed approach is correct and feasible.