
Control of Converter-Fed Induction Motor Drives 21-31
21.7.3.2 Modied ST-DTC
Many
m
odications
o
f
t
he
b
asic
S
T-DTC
s
cheme
a
imed
a
t
i
mproving
s
tarting,
o
verload
c
onditions,
v
ery-low-speed
o
peration,
to
rque
r
ipple
r
eduction,
v
ariable
s
witching
f
requency
f
unctioning,
a
nd
n
oise-
level attenuation have been proposed during the last decade.
During
s
tarting
a
nd
v
ery-low-speed
o
peration,
t
he
b
asic
S
T-DTC
s
cheme
s
elects
m
any
t
imes
t
he
z
ero
voltage vectors resulting in ux-level reduction, owing to the stator resistance drop. is drawback can
b
e avoided by using either a dither signal or a modied switching table [4,26].
Torque ripple reduction can be