부산대학교 도서관

This paper presents a modified topology of the neutral-point-clamped converter. The main change consists on adding a fourth leg, which is based on the flying-capacitor converter structure. The aim of this additional leg is to provide fault tolerance to the converter. Furthermore, during normal operation mode, this leg is able to provide a stiff neutral voltage. Consequently, the low-frequency voltage oscillations that appear in the neutral point of the standard three-level topology for some operation conditions no longer exist. As a result, the modulation strategy of the three main legs of the converter does not have to take care of voltage balance, and it can be design to achieve optimal output voltage waveforms, as well as to improve efficiency of the converter. Some simulation results are presented to show viability of this approach under both, normal operation mode and fault event. Experimental results are expected to include in the final paper.