Optimized Asymmetrical Switching Sequences-Based Model-Predictive Control for Three-Level T-Type Inverters

This article proposes a novel model-predictive control (MPC) based on optimized asymmetrical switching sequence (OASS-MPC) for three-phase three-level T-type inverters. The proposed OASS-MPC takes into account three essential aspects: the grid current quality, the switching loss, and the dc-link capacitor voltage balancing. In the OASS-MPC, the switching state transitions only occur at one moment during each control cycle. In addition, a voltage vector (VV) sequential switching strategy based on consecutive control cycles is proposed to reduce the switching frequency for the asymmetrical switching sequences (SSs), which reduces the switching frequency by half compared to symmetrical SSs. Moreover, three VV duty-cycle calculation methods are investigated to reduce the total harmonic distortion (THD) of the grid current. Furthermore, to avoid the cumbersome process of adjusting the weighting factors, OASS-MPC adopts a single-objective cost function, and the capacitor voltages are balanced by the redundancy characteristics of small VVs. Finally, the simulation and experimental results show a good performance for the OASS-MPC, in steady-state and transient response, with better current quality at the same average switching frequency compared to previously reported MPC strategies.