Page 83 - Hybrid-Renewable Energy Systems in Microgrids

Multilevel inverters: an enabling technology 67

H-bridge multilevel converter contains some SDCS. Modularity in control, modula-
tion, and protection requirements of each bridge are the advantages of this topology.
It should be noted that, compared to the neutral point-clamped and flying-capacitor
topologies, separated DC sources are required for each and every H bridge in each
phase [8].
Fig. 4.5 shows the power circuit for single phase leg of a nine-level inverter with
four H bridges in each phase. The resulting phase voltage is generated by the summa-
tion of the voltages generated by the different H bridges. Each single-phase full-bridge
inverter produces three voltages at the output: V DC ,0, and −V DC . This is done by con-
necting the capacitors in succeeding order to the AC side through four power switches.
The resulting output AC voltage oscillates from 4 to 4 with nine levels, and the stepped
waveform resembles sine wave, even without filtering.
Cascaded multilevel inverter (CMLI) is one of the most prominently used topology
among the multilevel inverters. The modularity and simplicity in its structure, when
compared to diode-clamped and flying capacitor type multilevel inverters make them
more important. Also it does not need any uniquely designed transformer as compared

Figure 4.5 Cascaded inverter circuit topology.