Neutral point potential balance of three-level inverter based on parameters self-tuning fuzzy logic control strategy

A significant problem with diode neutral point clamped (NPC) three-level inverter is the fluctuation in the neutral-point voltage. In this paper, the causes of the neutral point potential unbalance based on space vector pulse width modulation (SVPWM) are analyzed. And then a strategy based on parameters self-tuning fuzzy logic control (FLC) is presented which could solve the problems of some commonly used control strategies. For time-variable nonlinear systems, this algorithm has better robustness and adaptability. Set the voltage difference between up capacitor and down capacitor of DC bus as the input of the proposed controller, then fuzzy calibration unit corrects the quantification factor of fuzzy controller in real time depending on the degree unbalance. At the same time, by changing fuzzy rule according to the degree unbalance and the neutral point´s current direction, the duration of small vectors action can be obtained. The effectiveness of the proposed control approach is verified by simulation and experiment results.