| Abstract |
Even though the neutral point potential (NPP) balance problem of three-level neutral-point-clamped(NPC) converters can be solved by the traditional methods based on nearest-three-vectors (NTV)PWM, a low frequency fluctuation in the NPP will appear, which makes the capacitor reductionbecome hard. The dual modulation waves method is used to overcome the low frequency fluctuation,but it is an open-loop way, which will cause the drift voltage problem of the NPP and increase theswitching frequency. Moreover, the control ability of the neutral point current is limited since thezero-sequence voltage is fixed. By removing the limit of the zero-sequence voltage and introducing anew degree of freedom, a novel NPP control of three-level NPC converters based on the searchoptimization is proposed in this paper. Fuzzing the boundary between the NTV-PWM and the dualmodulation waves method, the proposed method realizes two modulations by a unified way. It cansolve the low frequency fluctuation problem, reduce the switching frequency and extend the controlability of the neutral point current simultaneously by choosing the optimal dual degrees of freedom.Comparing the NTV-PWM, the dual modulation waves method and the proposed method, thesimulation results verify the correctness and effectiveness of the proposed method. |
