Extended Period Control Approach FCS-MPC for Three Phase NPC Power Converters

Finite control set model predictive control (FCS-MPC) selects a voltage vector state at fixed sampling period without the use of a modulator. As a direct consequence, the conventional implementation of FCS-MPC presents variable switching frequency. Period control approach (PCA-FCS-MPC) for a two-level three-phase inverter is effective in controlling the switching frequency without the need of a modulation stage. However, its implementation for a three-level three-phase inverter is not straightforward due to the need for synchronizing the commutation of all the power semiconductors in each leg. This work presents a new method to implement this strategy in a three phase three-level neutral point clamped voltage source inverter (NPC-VSI), named direct grouping, which modifies the approach of PCA such that its implementation becomes possible on the NPC-VSI. This new method, along with a state-of-the art solution, are analyzed in detail to establish a metric for the evaluation of their performance, from which the new proposal shows improved outcome. Experimental results validate the switching frequency control performance, flexibility, and efficacy of the proposed strategy.