Page 88 - Hybrid-Renewable Energy Systems in Microgrids

72 Hybrid-Renewable Energy Systems in Microgrids

(DVRs), and unified power flow controllers (UPFCs) can impart instantaneous and
variable reactive power in response to grid voltage transients, increasing the grid
voltage stability. Due to the harmonic spectrum requirements from the energy pro-
viders and the need to overcome the voltage sags imposed by the grid codes all over
the world these devices (AF, STATCOMs, DVRs, and UPFCs) are recently gain-
ing importance. As examples, the diagram of a three-level diode-clamped converter
working as a STATCOM and a scheme of a multilevel inverter working as a UPFC
are shown in Figs. 4.9 and 4.10, respectively. Other applications comprise utility
adapters, for example, to connect a three-phase grid of 50 Hz and a single-phase grid
of 16 2/3 Hz for railway application.

4.2 Production
Multilevel inverters are widely used in any medium-voltage high-power motor drive
application. They have enlarged their presence in the petrochemical industry (pumps
and compressors), cement industry (high power fans), metal industry (steal rolling
mills), and mining industry (copper grinding mills and conveyors for ore transporta-
tion), among others [12].
Regenerative conveyors: In the mining industry, downhill conveyors are utilized as
a substitution to transport the ore originated in the mine to another mining process.
The system works continuously regenerating. It needs a power drive that permits this

Figure 4.9 STATCOM based on a three-level diode-clamped topology.