[58–68] and the systematic investigation towards increasing the
performance are cited in [69].
3. Machine control
In HEES, power electronic control technology serves the
machines to run effectively. Initially in hydroelectric generating
stations, induction machines are hardly preferred than synchronous
machines due to its unsatisfactory performance [70,71].
Recently, PE cascaded converter is employed between the slipring
terminals of wound-rotor induction machine and the utility
grid to control the rotor power [72]. This modified induction
machine is known as doubly fed induction machine (DFIM) in
which the rotor power control gives better performance characteristics
as well as reduce the rating of power converters. But,
controlling the DFIM is more complex than controlling the
standard induction machine. Here, contribution of flexible power
controllers makes the machine control easier and gives better
performance to DFIM. The recent growth of PE converters has
reincarnated the doubly fed induction machine by replacing
cycloconverter with 3-level VSI cascade back-to-back converter
[73–75]. The DFIM with PWM back-to-back converter are preferred
in hydroelectric power plants to interface electrical utility at
variable speed operation which decreases the mechanical stress
and acoustic noise thereby improves the power quality [76–78].
Overall, power electronics converters replace the mechanical
controls to provide dynamic response and fast recovery during