Switching angles and DC link voltages optimization for multilevel cascade inverters

The optimization of both DC link voltages and switching angles of fundament al switching strategy for the output waveform of a multilevel cascade inver ter is investigated in this study. Previous work in the area of fundamental switching for multilevel inverters is highlighted by the pulse width optim ization technique, where the switching angle at each voltage level is optim ized so that the resulting staircase output voltage has the minimum harmoni c content. The DC link voltage of each level, however, is assumed to be the same and constant. As an extension to this work, the optimization of both DC link voltages and switching angles of the staircase output voltage is ca rried out. Harmonic performance of the proposed switching strategy is simul ated and results are compared with that of the previous work. It is confirm ed theoretically that substantial improvement in the harmonic minimization can be obtained. In practice, the proposed method is especially suitable for the control of multilevel cascade inverters, the latest development of its kind, where eac h DC voltage can be self-maintained and independently controlled. The descr iption of the multilevel cascade inverters for applications of AC drives, a s well as Static Var Generation, is also given in this article.