
18-16 Power Electronics and Motor Drives
Note that, taking into account these considerations, P and Q are linearly dependents on and E. is
a
pproximation is true if the output impedance is not too large as in most practical cases.
In
d
roop
m
ethod,
e
ach
u
nit
u
ses
f
requency
i
nstead
o
f
p
hase
to
c
ontrol
t
he
a
ctive
p
ower
ows,
b
ecause
t
hey
d
o
n
ot
k
now
t
he
i
nitial
p
hase
v
alue
o
f
t
he
o
ther
u
nits.
H
owever,
t
he
i
nitial
f
requency
a
t
n
o-load
c
an
b
e
e
asily
xed
a
s
ω*
.
A
s
a
c
onsequence,
t
he
d
roop
m
ethod
h
as
a
n
i
nherent
t
rade-o
b
etween
t
he
a
ctive
p
ower
s
haring
a
nd
t
he
f
requency
a
ccuracy,
t
hus
r
esulting
i
n
f
requency
d
eviations.
I
n
[
Chandorkar94],
f
requenc ...