Two Effective Spectrum-Shaped FCS-MPC Approaches for Three-Level Neutral-Point-Clamped Power Converters

Unlike pulse width modulation (PWM) based approaches, the spectra of classical finite control set model predictive control techniques spreads uniformly across a wide frequency range for power converters, which makes the design of their filters particularly difficult. An effective method to achieve spectra similar to those of PWM for two-level power converters is the so-called model predictive period control (MPPC) approach, which makes the frequency of the converter's output voltage quasi-fixed by adding a constraint on the switching frequency. In terms of output voltage change, voltage-state-change (VSC) is more relevant than switch-state-change (SSC) because the output voltage change is unequal to that of SSC for multi-level power converters. In this work we propose two different control techniques, namely, switch-state-change (SSC-MPPC) and voltage-state-change based model predictive period control (VSC-MPPC), for 3L-NPC power converters. Simulation data confirm that, i) both approaches achieve current spectra similar to those of PWM-based solutions, ii) both of them achieve quasi-fixed switch frequency, which simplifies the heat sink design, however, VSC-MPPC practically operates with half of the reference frequency for 3L-NPC converter, iii) SSC-MPPC outperforms the VSC-MPPC approach in terms of power quality and neutral point voltage regulation but consumes much more switching losses especially for high level power systems.