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

Mendes introduced a monitoring technique for fault diagnosis in a CID based on Park’
vector approach [17, 18], namely average Park’s vector. Peuget also proposed a fault
detection and isolation on a CID [19], called current-vector trajectory. Basically, Mendes
and Peuget used input motor currents as diagnostic signals and modified the original
Clark and Park transform method as fault feature extraction to rate input motor current
signals as an important characteristic in order to classify a fault location in an inverter.
The difference between Mendes’s work and Peuget’s work is the diagnostic paradigm to
indicate fault locations (power switch of an inverter).
First, Mendes used average current Park’s vector ( Ia,av , Ib,av , and Ic,av ) to detect a fault.
The corresponding Park’s vector can be expressed as follows:
I
I
I
d , av
d , av
q,
av
∠θ
=
=
av
2
3
1
2
= I
I
I
a,
av
a,
av
d , av
−
−
+
28
1
6
1
2
j I
I
q
I
,
b,
av
c,
av
.
−
1
6
I
c,
av
,
(2.6)
The input motor currents are average value over one period. The magnitude and phase
angle of the average vector (Id,av , Iq,av) can be calculated in the complex coordinate.
Obviously, the average current vector in orthogonal space runs in a circuit will be zero
for a normal condition of a CID. In contrast, the magnitude of the vector will not be zero
if a fault occurs; normally, the magnitude will exceed some threshold value. The average
phase angle can be used to identify a fault location. Trajectories of Park’s vector
corresponding with the inverter switch locations (Figure 2.3) are illustrated in Figure 2.5.