Research On Fluctuation Of Neutral Point Potential In Three-Level Neutral-Point-Clamped Inverter

Since it's introduction in 1981 by A.Nabae, the three-level neutral-point-clamped (NPC) voltage source inverter (VSI) has been widely used. The applications of this technology not only include high-capacity high-performance inverters, but also include static VAR compensation systems, active filtering, as well as applications in power conditioning systems. But this technology also has its disadvantages: The complexity of the controller is significantly increased and the balance of the neutral-point has to be assured. What's more, the fluctuation in the neutral-point voltage is a significant problem.The main work and contributions of dissertation are summarized as follows:Firstly, the negative impact of fluctuation in the neutral-point voltage of three-level NPC inverters was introduced and the cause of fluctuation in the neutral-point potential was analyzed objectively in the dissertation.Secondly, it was discussed in this paper that traditional neutral-point voltage balancing control methods had many advantages and disadvantages by comparatively analysis of carrier-based PWM scheme and space vector PWM scheme.On the base of above work, the effect to the space vector PWM scheme caused by the fluctuation of neutral point potential was discussed and what's more the order of space vectors is rearranged for every triangular regions.Finally, the novel modulation was proved by MatLab 7.0 / Simulink simulation.