Dc-link capacitor voltage control for the NPC three-level inverter with a newly MPC-based virtual vector modulation

Dc-link capacitor voltage unbalance would affect the performance of the neutral-point clamped (NPC) three-level inverter. With the traditional virtual space vector modulation (VSVPWM) method, the dc-link capacitor voltage could be kept balance under the different modulation indexes or power factors. With the virtual medium vector being set as an adjustable one, the voltage balance could be better guaranteed no matter there might have some non-linear factors However, whether the traditional or improved VSVPWM method has a complicated trigonometric calculation, thus, a newly MPC-based virtual vector modulation has been proposed in this paper. With the 19 virtual space vectors being in roll optimisation, a nice current trajectory, dc-link capacitor voltage balance, even a relative low switch losses have been implemented. Considering that the optimised virtual space vector could not be taken as a direct output, the distribution of the basic vectors has been generated to make it being favourable for modulation. The effectiveness of this MPC-based virtual vector modulation is verified in comparisons with other methods, which can save over 67.3% execution time of the traditional SVPWM method, and over 46.6% of the improved VSVPWM way while provide a better dc-link capacitor voltage balance and output current quality.