Page 87 - Hybrid-Renewable Energy Systems in Microgrids

Multilevel inverters: an enabling technology 71

several tens of megawatts, it is anticipated to increase with photovoltaic technology
evolution and cost reduction. Here multilevel inverters can also become admissible,
since PV strings can be utilized as DC sources for multilevel topologies. As there is
no exigency for a rectifier stage, the multilevel power circuit is greatly miniaturized.
In addition, the multilevel inverter can impart control for both input power factor and
maximum power tracking. Moreover, it evades or averts the use of a filter, can enhance
efficiency (lower switching frequencies can be utilized), can eradicate the need for
step-up transformers, or increment elevator circuits if enough PV sources can be con-
nected in series. Several circuits using cascaded H-bridge (CHB) connected to the grid
have been derived and cited for PV power conversion. Fig. 4.8 illustrates grid connec-
tion of PV system using CHB.
On the other hand, an actual problem of the electrical grid is the power-distribution
control and management. In this scenario, FACTs have been introduced as the solu-
tion to enhance the controllability and the power transfer capability of the network.
Among the many different technologies covered by FACTs, the most interesting one
for multilevel inverters is in distributed energy applications, where the advancements
of active filters (AFs), static compensators (STATCOMs), dynamic voltage restorers

Figure 4.7 Three-level NPV back-to-back for wind energy conversion.

Figure 4.8 Grid connection of PV system using CHB.