Fault Diagnostic System for Cascaded H-Bridge Multilevel Inverter ...

i
i
i
α
β
2 1
= ia
− ( ib
+ ic
) ,
3 3
=
=
1
( i
3
1
( i
3
26
),
0 a b c
b
− i
+ i
c
+ i
where iα and iβ are components in an orthogonal space,
io is a homopolar component of the system,
ia,ib,and ic are components in original space.
Assuming that the CID has a balanced load: ia+ib +ic = 0, iα and iβ can be rewritten as:
i
i
i
α
β
a
= i
=
+ i
,
1
i
3
b
a
a
+ i
c
+
=
0.
),
2
i
3
b
,
(2.1)
(2.2)
The transformation from a two-phase orthogonal α, β space to a three-phase stationary
component is performed by
i
i
i
a
b
c
=
i
α
,
1
= − i
2
1
= − i
2
α
α
+
−
3
2
i
3
i
2
β
β
.
,
(2.3)
The components of two-phase orthogonal α, β space can be fed to a vector rotation block
where it rotates over an angle (θ ) to follow the frame d, q attached to the rotor flux by
using Park transform:
i
i
sd
sq
= i
α
= − i
cos
α
() θ + iβ
sin () θ ,
() θ + i cos().
θ
sin
β
(2.4)