Optimal Two Degrees-of-Freedom Based Neutral Point Potential Control for Three-Level Neutral Point Clamped Converters

다국어 초록 (Multilingual Abstract)

Although the dual modulation wave method can solve the low-frequency neutral point potential (NPP) fluctuation problem forthree-level neutral point clamped converters, it also increases the switching frequency and limits the zero-sequence voltage. Thatmakes it harmful when dealing with the NPP drift problem if the converter suffers from a long dead time or asymmetric loads.
By introducing two degrees of freedom (2-DOF), an NPP control based on a search optimization method can demonstrate itsability to cope with the above mentioned two types of NPP problems. However, the amount of calculations for obtaining anoptimal 2-DOF is so large that the method cannot be applied to certain industrial applications with an inexpensive digital signalprocessor. In this paper, a novel optimal 2-DOF-based NPP control is proposed. The relationships between the NPP and the2-DOF are analyzed and a method for directly determining the optimal 2-DOF is also discussed. Using a direct calculationmethod, the amount of calculations is significantly reduced. In addition, the proposed method is able to maintain the strongestcontrol ability for the two types of NPP problems. Finally, some experimental results are given to confirm the validity andfeasibility of the proposed method.

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