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Multilevel inverters: an enabling technology 79

in each individual string, manufacturer, and so on), different size or different technol-
ogy, and strings with different orientations (east, south, or west), inclination or shad-
owing, can be linked to one common inverter, while each working at their individual
maximum power point. Convincingly the multi-string inverter topology incorporates
higher energy generated in the string inverter with the reduced capital investment of
the central inverter topology. Considerable number of PV strings, each having a single
dedicated DC–DC converter, are associated to a central inverter. Likewise in addition
to the conventional two-level inverters, neutral-point-clamped (NPC) inverter is being
incorporated for central inverter, string inverter, or multi-string inverter topologies.
Presently, cascaded H-bridge multilevel inverter topology is being addressed by many
researchers for PV system applications [18]. It is featured by a cascade connection of
a few H-bridge inverters per phase. The system topology is illustrated in Fig. 4.15.
A single PV panel can be precisely connected to the DC side of individual H bridge
inverter to accomplish the concept of a single converter per one PV panel. This is
analogous to that of the module integrated inverter topology. In this situation, it is pos-
sible to actualize the distributed MPPT control by each H-bridge inverter separately,
that enormously optimizes the energy generated from the PV panels.

5 Conclusion

Multilevel inverters have developed from being an evident technology to a well-
entrenched and attractive solution for high and medium voltage power applications.
Various topologies and several modulation methods have found industrial application.
Initially, the higher power rates together with the improved power quality have been
the major market drive and trigger for research and development of multilevel invert-
ers. Fundamental multilevel inverter structures including the advantages and disad-
vantages of each technique have been discussed in this chapter. The main advantage
of MLI family is that it finds a solution to the problems of total harmonics distortion,
electromagnetic interference (EMI), and dv/dt stress on each switch. Research works
are in progress considering the structure complexity and control circuits. However,
the continuous development of technology and the evolution of industrial applications
will open new challenges and opportunities that could motivate further improvements
to multilevel inverter technology. A review on multilevel inverters, their topologies
and applications have been carried out in this chapter.

References

[1] Rodiguez, J., Lai, J.S., Peng, F.Z., 2002. Multilevel inverter: a survey of topologies, con-
trols, and application. IEEE Trans. Ind. Elect. 49 (4), 724–738, Jul./Aug.
[2] Rodriguez, et al., 2009. Multilevel converters: an enabling technology for high-power
applications. Proc. IEEE 97 (11), 1786–1817, November.
[3] Tolbert, L.M., Peng, F.Z., Habetler, T.G., 1999. Multilevel converters for large electric
drives. IEEE Trans. Ind. Appl. 35, 36–44, Jan. /Feb.