CERUS CI-007-P2 - Checking VFD Power Components; Diode Bridge and IGBT Module Test (7.5-40 HP); Diode Bridge and IGBT Module Test (50-700 HP)

Chapter 8 - Troubleshooting & Maintenance
8-4
 Check diodes in the rectifier bridge and IGBT module with multimeter in the sequence shown in
below table and diagram. Diode state codes: C- Closed and O- Open.
8.4.2 Diode Bridge and IGBT Module Test for 50~700HP VFDs
Before checking the power components, disconnect AC input power and wait for about 10 minutes.
 Check that there is no DC voltage on P1+ and N- terminals.
 Disconnect power wires from R, S, and T terminals and motor leads from U, V, and W terminals.
 Check diodes in the rectifier bridge and IGBT module with multimeter in the sequence shown in
below table and diagram. Diode state codes: C- Closed and O- Open.
Note: The 50-700HP VFDs have half controlled rectifier bridge with SCRs (silicon controlled rectifier).
The SCR cannot be checked for open state with multimeter. The reading from R to P1 terminals will
represent charge diode and resistor circuit. Terminals S and T to P1 will show closed state in direct and
reverse test if SCRs are not shorted.
Black
Lead to
P1
+
Black
to
N
Red
to
P1
+
Red
to
N
Red
to
R S T R S T
Black
to
R S T R S T
State
O
O
O
C
C
C
State
C
C
C
O
O
O
Red
to
U
V
W
U
V
W
Black
to
U
V
W
U
V
W
State
O
O
O
C
C
C
State
C
C
C
O
O
O
Charge
Resistor
M/C Contact
R
S
T
U
V
W
+
++
+
DC Bus
Capacitors
DC Bus Positive
(P1+)
(N-) DC Bus Negative
IGBT transistors
Six- Pulse
Rectifier Bridge
Charge Diode and Resistor
SCRs
DIODES
R
S
T
U
V
W
+
++
+
DC Bus
Capacitors
DC Bus Positive
(P1+)
(N-) DC Bus Negative
IGBT transistors