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 reduction become 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 the switching frequency. Moreover, the control ability of the neutral point current is limited since the zero-sequence voltage is fixed. By removing the limit of the zero-sequence voltage and introducing a new degree of freedom, a novel NPP control of three-level NPC converters based on the search optimization is proposed in this paper. Fuzzing the boundary between the NTV-PWM and the dual modulation waves method, the proposed method realizes two modulations by a unified way. It can solve the low frequency fluctuation problem, reduce the switching frequency and extend the control ability 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, the simulation results verify the correctness and effectiveness of the proposed method.
Published Version
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