An Improved Finite Control Set Model Predictive Control with Complete Control of Flying-Capacitor Voltages for Four-Level Nested Neutral-Point Clamped Inverters

This article introduces an enhanced FCS-MPC technique that allows for full control of flying capacitor (FC) voltages in a four-level inverter. This method reduces the computational burden, decreases harmonic currents, and ensures balanced FC voltage levels. Firstly, the vector in the a-b-c coordinate system is converted to the g-h coordinate system. Then determine the region where the reference voltage vector is located, and the four-level vectors are converted into a two-level sector for calculation. Next, the influence of the switching state corresponding to the redundancy vector on the FC is analyzed, and the switching states which makes the FC voltage balance are selected. Finally, the duty cycle of the three basic voltage vectors is computed by the distance between the reference vector and the fixed vectors in the space vector diagram. The steady-state and the dynamic simulations are conducted to verify the effectiveness of the proposed FCS-MPC method.