2016 Volume 13 Issue 23 Pages 20160978
The three-level neutral-point-clamped (NPC) inverter, which is a widely used topology of grid-connected multilevel inverters, suffers the drawback of the NP voltage drift. This paper introduced an improved predictive direct current control strategy to improve grid-connected current quality of the system. The proposed strategy uses the nearest-three-virtual-vector (NTV2) modulation strategy which can get rid of the NP voltage balance problem for any range of inverter output voltage. Since the disadvantages of a lot of calculation for NTV2 algorithm in real-time control, the vectors in other sextants are mapped into the first sextant by a simple coordinate transformation. The time derivatives of currents for each selected vectors are used to get the application times that minimize objective function. In addition, comparing with SVPWM approaches the proposed strategy have a constant switching frequency and better line current total harmonic distortion (THD), its validity is verified by the simulation and experiment.